Let’s dive into the process of creating these delectable bars. Follow these simple steps:

1. Preheat your oven to 350°F (175°C) and line an 8×8-inch baking dish with parchment paper, leaving an overhang on the sides for easy removal.
2. In a large bowl, combine the flour, oats, granulated sugar, brown sugar, baking powder, and salt. Stir in the melted butter until the mixture is crumbly.
3. Press two-thirds of the oat mixture evenly into the bottom of the prepared baking dish to form the crust. Reserve the remaining mixture for the topping.
4. In another bowl, whisk together the sweetened condensed milk, lemon juice, lemon zest, and vanilla extract until smooth.
5. Pour the lemon mixture over the crust, spreading it evenly with a spatula. Sprinkle the reserved oat mixture over the top.
6. Bake in the preheated oven for 25-30 minutes, or until the top is lightly golden and the filling is set.
7. Allow the bars to cool completely in the pan on a wire rack before lifting them out using the parchment overhang. Slice into bars and enjoy!

These bars have taught me the importance of patience — letting them cool completely ensures they hold together perfectly when cut.