Heat oven to 190C/170C fan/gas 5. Butter a 12-hole madeleine mould (use a tiny amount of the melted butter) and dust lightly with flour. You can use tartlet tins if you don't have the a madeleine mould.
Mix the flour and sugar in a bowl. Put the butter, egg yolk, honey and vanilla into a separate bowl and whisk with a fork to mix. Whisk the two egg whites until stiff. Fold the butter mixture into the dry ingredients until evenly mixed, then fold in the egg whites in two batches using the whisk.
Divide between the prepared moulds and bake for 10-12 mins until golden brown and firm to the touch. Leave to cool in the moulds for a few mins, then turn out and cool on a wire rack. Dust with icing sugar before serving.