Preheat your oven to 350°F (177°C) and line an 8-inch square baking pan with parchment paper.

In a large mixing bowl, combine 7 tablespoons of softened unsalted butter with 3/4 cup of packed brown sugar and beat until smooth, then add 1 teaspoon of pure vanilla extract.

Gradually mix in 1 cup of all-purpose flour, 1 teaspoon of baking powder, 1/4 teaspoon of salt, and 1 cup of oats until crumbly.

Press slightly more than half of the mixture into the prepared pan to form a crust and bake for about 12 minutes until lightly golden.

While the crust bakes, whisk together 14 ounces of sweetened condensed milk, 6 tablespoons of fresh lemon juice, and 1 tablespoon of lemon zest until smooth.

Once crust is out of the oven, pour the lemon filling over it and spread evenly, then sprinkle the remaining crumble mixture on top.

Bake the assembled bars for an additional 22-25 minutes until edges are golden and center is slightly firm.

Once baked, cool for at least 20 minutes, lift out using parchment paper, slice into squares, and enjoy!