While the crust is baking, mix 1⁄4 cup flour, 11⁄2 cups powdered sugar, 1⁄4 teaspoon salt, eggs, lemon juice, yogurt, baking powder, and lemon zest in a large bowl with a mixer. Beat until smooth. Pour the lemon mixture on top of the hot cookie crust and return to oven. Bake for 35 minutes, until the topping is set and edges are light brown. Cool thoroughly in the pan. Sprinkle with extra powdered sugar, if desired, before serving. To store, cover and refrigerate for 3–5 days.