Beat the eggs, sugar, lemon zest, and vanilla together in a mixing bowl until light colored and fluffy, about 10 minutes. Pour in the milk and cream; continue beating to make a smooth mixture. Stir in the ricotta cheese and cherries until evenly blended. Pour into the pie shells.
Bake in preheated oven for 10 minutes. Reduce heat to 165 degrees C (325 degrees F), and bake until set, about 50 minutes more. Cool on racks. When pies are completely cool, dust with icing sugar, and decorate by placing 1 whole cherry in the center of each pie.