Preheat your oven to 350 degrees F. Line an 8×8 inch baking pan with parchment paper, leaving an overhang on two sides for easy removal.
Prepare the crust: In a medium bowl, combine the flour, 1/2 cup granulated sugar, and salt. Cut in the cold butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.
Mix in the egg yolk and vanilla extract until the dough just comes together. Press the dough evenly into the bottom of the prepared pan to form the crust. Bake the crust for 15 minutes until lightly golden.
While the crust bakes, prepare the filling: In a large bowl, whisk together the drained ricotta cheese, 1/2 cup powdered sugar, the egg, lemon zest, and cinnamon until smooth. Stir in the mini chocolate chips and candied orange peel, if using.
Pour the ricotta filling evenly over the warm, pre-baked crust.
Return the pan to the oven and bake for 30 to 35 minutes, or until the filling is set and the edges are lightly browned. The center should not jiggle significantly when gently shaken.
Let the squares cool completely in the pan on a wire rack. This cooling process is important for the filling to set fully.
Once cool, lift the squares out of the pan using the parchment overhang. Cut into 16 squares. Dust generously with extra powdered sugar before serving.
Notes
Drain your ricotta thoroughly by placing it in a fine-mesh sieve lined with cheesecloth over a bowl in the refrigerator for at least 2 hours, or overnight. This prevents a watery filling.
For a richer flavor, substitute 1/4 cup of the granulated sugar in the crust with light brown sugar.
If you prefer a slightly firmer texture, chill the finished squares for at least 2 hours before slicing.