To make Martha Stewart madeleines, start by preheating the oven and greasing a madeleine pan with butter and flour. Next, whisk together flour, baking powder, and salt in a bowl. In a separate bowl, beat together eggs and sugar until light and fluffy, then fold in vanilla and lemon zest. Gradually add in the flour mixture, followed by melted butter. Chill the batter for at least 30 minutes, then use a spoon or pastry bag to fill each madeleine mold about 3/4 full. Bake the madeleines for 10-12 minutes, until the edges are golden brown and the centers spring back when lightly touched. Let cool in the pan for a few minutes, then transfer to a wire rack to cool completely. Dust with powdered sugar before serving.