Whisk the condensed milk, melted butter, milk, yogurt, sugar, vanilla and lemon zest in a bowl.
Sift the flour, baking powder, baking soda and salt over the wet ingredients and fold just until smooth.
Cover the batter and chill for 1 hour. The cold batter helps create the signature hump.
Preheat the oven to 375 F. Brush a madeleine pan generously with butter and dust lightly with flour.
Spoon 1 tablespoon of batter into each shell without spreading it.
Bake for 10 to 12 minutes, until the humps rise and the edges turn golden.
Tap the madeleines out onto a rack, dust with powdered sugar and serve warm.
