Gluten free madeleines

Madeleines

• 120 g unsalted butter, cut into pieces
• 2 eggs
• 120 g caster sugar
• 1 lemon, zest only, no white pith
• 1 tsp natural vanilla extract
• 30 g milk
• 10 g oil
• 120 g gluten free flour
• 1 ½ tsp gluten free baking powder
• 1 pinch sea salt
• icing sugar, to dust