These Lemon Oatmeal Crumble Bars are sunshine in a pan. A buttery brown sugar and oat crumble makes both the crust and the topping, and tucked in the middle is a creamy, tangy lemon filling made with just three ingredients. Sweet, tart, chewy, and crumbly, every bite has a little bit of everything.
They’re simple enough for a weeknight treat but pretty enough for a bake sale, a baby shower, or a spring brunch. And because the filling is made with sweetened condensed milk, there’s no fussing with a stovetop lemon curd. Just whisk and pour.
If you love easy bars and baked goodies, be sure to check out my other dessert recipes.
Why You’ll Love This Recipe
- One crumble, two jobs: The same oat mixture makes the crust and the topping.
- Three-ingredient filling: Sweetened condensed milk, lemon juice, and lemon zest. That’s it.
- The perfect balance: Brown sugar sweetness and bright lemon tang in every bite.
- Easy to double: Bake a big 9×13 pan for a crowd.
- Freezer-friendly: They keep for up to 3 months in the freezer.
Ingredients Breakdown
Here’s what goes into these lemon crumble bars. You’ll find exact amounts in the recipe card at the bottom of the page.
- Unsalted butter: Softened to room temperature so it beats smoothly with the sugar.
- Brown sugar: Light or dark both work. It gives the crumble a rich, caramel-like flavor.
- Vanilla extract: Adds warmth to the crumble.
- All-purpose flour: Spooned and leveled, so you don’t pack in too much.
- Baking powder and salt: For a little lift and balance.
- Oats: Old-fashioned or quick oats work, but not instant. They give the bars their chewy, hearty texture.
- Sweetened condensed milk: Full-fat only. It’s what makes the filling thick and set. Don’t use evaporated milk or fat-free.
- Lemon juice and zest: Fresh lemons give the brightest flavor. You’ll need about 2 lemons.
Step-by-Step Instructions
1. Prep the pan
Preheat your oven to 350°F (177°C). Line an 8-inch square baking pan with parchment paper so the bars lift out easily.
2. Make the crumble
Beat the softened butter and brown sugar with a mixer on medium-high until fully combined, about 1 minute. Scrape down the bowl, add the vanilla, and beat for 30 seconds more. Add the flour, baking powder, salt, and oats and mix on medium speed until combined. It’ll be dry and crumbly, about 3 to 3 1/2 cups in all.
3. Bake the crust
Press slightly more than half of the crumble into the bottom of the pan. Bake for 12 minutes.
4. Mix the lemon filling
While the crust bakes, whisk the sweetened condensed milk, lemon juice, and lemon zest in a medium bowl until smooth and thick.
5. Layer it up
Pour the lemon filling over the hot crust and spread it out evenly. Sprinkle the rest of the crumble over the top.
6. Bake again
Bake for another 22 to 25 minutes, until the edges are lightly golden and the center is set. Be careful not to over-bake.
7. Cool and cut
Let the bars cool completely in the pan on a wire rack. Then lift them out using the parchment and cut them into squares.
Tips and Variations
- Use full-fat sweetened condensed milk: Evaporated milk or fat-free versions won’t set properly.
- Give the crust a little extra: Use slightly more than half the crumble for the bottom so it holds together.
- Pour onto a hot crust: Adding the filling right after the crust comes out of the oven helps the layers bake together.
- Cool completely before cutting: The filling needs to firm up for clean squares.
- Double the batch: Double everything and bake in a 9×13-inch pan. Pre-bake the crust for 18 minutes, then bake the filled bars for 35 minutes, or until set.
- Dust with powdered sugar: A light sprinkle just before serving makes them extra pretty.
How to Serve This Recipe
Cut the bars into squares and serve them at room temperature or slightly chilled. A light dusting of powdered sugar makes them look bakery-perfect.
They’re lovely on a spring dessert table next to Lemon Blueberry Sheet Cake and a plate of Soft Mini Lemon Cookies with Lemon Glaze. They also make a sweet finish after a light dinner like Grilled Lemon Chicken.
Frequently Asked Questions
Can I use evaporated milk instead of sweetened condensed milk?
No. You need full-fat sweetened condensed milk for the filling to set. Evaporated milk and fat-free versions won’t work.
What kind of oats should I use?
Old-fashioned or quick oats both work. Don’t use instant oats.
How do I know when the bars are done?
After adding the filling and topping, bake for 22 to 25 minutes, until the edges are lightly golden and the center is set.
How do I store lemon crumble bars?
Keep leftovers at room temperature for up to 2 days, or refrigerate them for up to 1 week.
Can I freeze them?
Yes. Freeze cut bars in a single layer, separated by parchment, in a freezer-safe container for up to 3 months. Thaw overnight in the fridge and bring to room temperature before serving.
You May Also Love
- Lemon Blueberry Pound Cake
- The Ultimate Lemon Sugar Cookies
- Best Key Lime Pie
- The Best Carrot Cake Bars
- No-Bake Chocolate Oatmeal Bars
Lemon Oatmeal Crumble Bars
Ingredients
For the Crust & Topping
- 7 tablespoons (99g) unsalted butter softened to room temperature
- 3/4 cup (150g) light or dark brown sugar packed
- 1 teaspoon vanilla extract
- 1 cup (125g) all-purpose flour (spooned & leveled)
- 1 teaspoon baking powder
- 1/4 teaspoon salt
- 1 cup (85g) old-fashioned oats or quick oats (not instant)
For the Lemon Filling
- 1 can (14 ounces) full-fat sweetened condensed milk
- 6 tablespoons (90ml) lemon juice (from about 2 lemons)
- 1 tablespoon lemon zest (from about 1 lemon)
Instructions
- Preheat the oven to 350°F (177°C). Line an 8-inch square baking pan with parchment paper so the bars lift out easily.
- Make the crumble: beat the softened butter and brown sugar with a mixer on medium-high until fully combined, about 1 minute. Scrape down the bowl, add the vanilla and beat for 30 seconds more. Add the flour, baking powder, salt and oats and mix on medium speed until combined. It will be dry and crumbly, about 3 to 3 1/2 cups in total.
- Press slightly more than half of the crumble into the bottom of the pan to make the crust. Bake for 12 minutes.
- While the crust bakes, whisk the sweetened condensed milk, lemon juice and lemon zest in a medium bowl until smooth and thick.
- Pour the lemon filling over the hot crust and spread it evenly. Sprinkle the rest of the crumble over the top.
- Bake for another 22 to 25 minutes, until the edges are lightly golden and the center is set. Be careful not to over-bake.
- Let the bars cool completely in the pan on a wire rack. Lift them out using the parchment and cut into squares.
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- Tips:
- Sweetened Condensed Milk: Make sure you’re using full-fat sweetened condensed milk (not evaporated milk) for the filling to set properly. Fat-free versions won’t work.
- Doubling the Recipe: You can easily double the recipe. Simply double all the ingredients and bake in a 9x13-inch pan. Increase the crust pre-bake time to 18 minutes, and bake the filled bars for 35 minutes, or until set.
- Storage: Keep leftover bars at room temperature for up to 2 days, or refrigerate for up to 1 week.
- Freezing: Freeze cut bars in a single layer, separated by parchment paper, in a freezer-safe container for up to 3 months. Thaw overnight in the fridge and bring to room temperature before serving.
