Place the butter in a saucepan over a medium heat until melted and foamy.
When the foam starts to clear, and you can see the milk solids turn brown and sink to the bottom, remove from the heat.
Quickly pour through a sieve lined with muslin or kitchen paper, into a bowl or jug to catch the milk solids.
Measure out 80 ml, (2.7 fluid ounces), of butter for the recipe.
Use any leftover butter to grease the financier moulds.
Place the flour, baking powder, sugar and salt if using into a large bowl and mix. Make a well in the centre.
Put the egg whites in a bowl and give them a quick whisk. Use a metal spoon to fold in the browned butter, vanilla and egg whites.
Pour the batter in the financier moulds until they almost reach the top and sprinkle the flaked almonds over.
Preheat the oven to 200 C / 400 F / 180 FAN / Gas 6 and bake for between 10 and 20 minutes. The almond financiers should be well risen, brown on the edges and springy to the touch.
If you are using a silicon mould allow them to cool for at least 5 minutes, then they should easily pop out to finish cooling on a wire rack.