Preheat oven to 350 F and grease a 9x9 square baking pan.
In bowl of your food processor, pulse to combine flour and sugar. Add vanilla extract and pulse two or three times to combine. Add butter all at once and process until coarse crumbs are formed, just as the dough begins to come together. Dump two-thirds of the crumb mixture into prepared pan and press evenly. Set remaining crumb mixture aside for the topping.
Spread lemon curd over the crumb crust. Sprinkle remaining topping over the curd.
Bake in preheated oven for 35-40 minutes or until edges are lightly browned.
Remove from oven to wire rack and allow to cool completely before cutting into squares.
For the glaze, add lemon extract, melted butter and one tablespoon of the milk to the powdered sugar. Stir to combine and add small amounts of remaining milk, as needed, until you reach a thick drizzling consistency. Drizzle over individual squares. Allow glaze to set before serving.