Preheat oven to 400°F (200°F). Generously grease Madeleine pan with shortening.
Sift flour and baking powder together into a bowl, set aside.
Combine eggs and sugar, beat until very pale yellow. Add butter, liqueur, and lemon zest, mix until well combined.
Add dry ingredients to mixing bowl of wet ingredients, stir until well incorporated and smooth.
Spoon 1 tablespoon (15 ml) of batter into each prepared Madeleine mold cavity. Bake for 10-12 minutes, or until golden. Turn Madeleines out onto a clean dishtowel, cool.
To serve, dust Madeleines with a little powdered sugar, or dip 1 end/side of each shell into melted chocolate.