Preheat the oven to 200C/400F/Gas 6. Brush the madeleine tray with melted butter then shake in a little flour to coat, tapping out the excess.
Whisk together the eggs and the sugar in a bowl until frothy. Lightly whisk in the remaining ingredients. Leave to stand for 20 minutes before carefully pouring into the prepared madeleine tray.
Bake for 8-10 minutes, or until the mixture has risen a little in the middle and is fully cooked through. Transfer the madeleines to a wire rack and leave for a few minutes to cool slightly. These are best eaten within an hour of cooking.
Any of these would work well: La Marca, Prosecco di Conegliano Valdobbiadene Extra Dry NV Italy; Villa Sandi Prosecco Frizzante DOC NV; La Jara Prosecco Frizzante Organic.