In a mixing bowl, combine flour, sugar, salt, butter, and baking powder. Work the mixture until it looks sandy. Next, add in the eggs and lemon zest; knead until smooth. Wrap the dough in plastic and refrigerate for 15-20 minutes.

In a saucepan, heat the milk with lemon zest until just boiling. In a separate bowl, whisk together egg yolks, sugar, and cornstarch until smooth. Slowly pour in the hot milk, whisking continuously, then return to heat. Cook on low, stirring until thickened.

Roll out the chilled pastry on a floured surface. Use a round cutter to cut discs for your tart molds. Press the pastry into the molds, trimming any excess edges, and prick the bottoms with a fork to prevent bubbling.

Pour the creamy custard into the pastry shells and create a decorative lattice topping with leftover pastry strips if desired. Bake in a preheated oven at 356°F for about 35 minutes or until golden brown. Allow them to cool before carefully removing from molds and dusting with powdered sugar.