Make the Crust and Topping
Heat the oven to 350°F (177°C). Use parchment paper to line an 8-inch square pan.
Beat butter and brown sugar at medium to high speed until combined.
Add vanilla extract, then beat on medium-high for 30 seconds. Add oats, baking powder, and flour. Beat on medium speed until combined.
Press slightly over half of the mixture into the prepared pan. Bake for 12-14 minutes.
Make the Lemon Filling
Whisk together sweetened lemon zest, lemon juice, and condensed milk.
Pour lemon filling over the hot pre-baked crust and spread evenly. Sprinkle the remaining crumble mixture over the top.
Bake it in the oven for about 23-25 minutes, until the edges get a bit of color and the filling is firm.
Cool completely on a rack before lifting from the pan and cutting into bars.
- Store at room temperature for 2 days or in the refrigerator for up to 1 week.
- For longer storage, freeze slices layered with parchment paper in a freezer-safe container for up to a few months.
- Do not use evaporated milk in place of the condensed milk. Half-and-half or heavy cream can be used in a pinch, but additional sugar will be needed.
Calories: 211kcal | Carbohydrates: 32.8g | Protein: 3.8g | Fat: 7.6g | Saturated Fat: 4.6g | Cholesterol: 21.7mg | Sodium: 102mg | Potassium: 144mg | Fiber: 0.8g | Sugar: 22.8g | Calcium: 101mg | Iron: 0.8mg