Preheat your oven to 375°F. This is a crucial step to ensure even baking. While the oven heats, you can prepare the rest of the ingredients.
In a small bowl, whisk together the sweetened condensed milk, lemon juice, and lemon zest. Make sure to mix them well until fully combined. Set this mixture aside as it will be the refreshing filling.
In another bowl, sift together the flour, baking powder, and salt. Sifting helps to aerate the flour and combine the dry ingredients evenly.
In a separate mixing bowl, use an electric mixer to cream the butter until it’s light and fluffy. Gradually blend in the brown sugar until fully incorporated. This step is essential as it creates the base for your crumb mixture.
Add the oats and the sifted flour mixture to the butter and sugar mixture. Mix until it becomes crumbly. You want to see some larger chunks of butter for added texture.
Spread half of this crumb mixture into the bottom of a greased 9x12-inch baking pan. Pat it down firmly with your hands or use the back of a measuring cup to ensure an even layer.
Pour the lemon mixture over the crumb base. Spread it evenly with a spatula, ensuring that every corner is covered.
Cover the lemon filling with the remaining crumb mixture, spreading it out evenly. Don’t worry if some of the lemon filling shows through; it’ll create a beautiful top!
Bake in the preheated oven for 20 to 25 minutes. Keep an eye on the edges; they should turn a lovely golden brown when done.
Once baked, allow the bars to cool in the pan at room temperature for about 15 minutes. This helps them set before cutting.
Cut into 2-inch squares and chill in the pan until firm. Removing them too early can cause them to fall apart, so patience is key!
Once firm, gently remove the squares from the pan. You can use a spatula for easier lifting. Enjoy your homemade Lemon Crumb Bars!
