1. Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan or line it with parchment paper for easy removal.
2. In a medium bowl, whisk together the flour, baking powder, and salt. This dry mix will give your squares a tender crumb.
3. In a large bowl, cream the softened butter and granulated sugar together until light and fluffy—about 3 to 4 minutes. This step adds air, making the cake layer nicely tender.
4. Add the egg yolks one at a time to the butter mixture, beating well after each addition. Stir in the vanilla extract and lemon juice for that bright flavor twist.
5. Slowly add the dry ingredients to the wet ingredients, mixing just until combined. Over-mixing can make the cake tough, so be gentle here.
6. In a separate bowl, beat the egg whites until stiff peaks form. This will help give the cake a light texture.
7. Fold the egg whites gently into the batter in three additions, trying not to deflate the mixture.
8. Pour half of the batter into the prepared pan and spread evenly with a spatula.
9. In another bowl, combine the ricotta, mascarpone (if using), orange zest, and mini chocolate chips. Stir until smooth and creamy.
10. Spread the ricotta mixture evenly over the batter in the pan.
11. Top with the remaining batter, spreading carefully to cover the filling without mixing layers.
12. Bake for 40 to 45 minutes, or until the top is golden and a toothpick inserted into the cake layer comes out clean (avoid poking the ricotta layer).
13. Allow the squares to cool completely in the pan on a wire rack. This step is key for clean slicing and full flavor.
14. Once cooled, dust generously with powdered sugar before cutting into squares.

One of my favorite tips I learned from those kitchen moments with Grandma is to let the dessert rest overnight if you can. The flavors meld beautifully, and the texture firms up just right, making each square a perfect bite of indulgence.