Preheat oven to 350°F (177°C). Grease and line an 8-inch square baking pan with parchment paper, leaving an overhang.,Make the crust: In a bowl, mix flour and sugar. Cut in butter until crumbly. Press mixture evenly into the pan. Bake for 25–28 minutes, or 20–23 minutes for a softer crust.,Prepare filling while crust bakes: Mix lemon zest and sugar together with a fork to release oils. Whisk in eggs, then stir in melted butter and lemon juice. Add flour and mix until smooth.,Pour the lemon filling over the hot crust and return to the oven. Bake for 12–15 minutes, or until the filling is set but still soft to the touch.,Cool at room temperature for 1½ hours. Lift out using parchment, cut into squares, and dust with powdered sugar before serving.