Place the butter in a saucepan over a medium heat and let it melt. Get a bowl ready and stand it on a heatproof service (a trivet or towel), you will pour the butter into this bowl to stop it cooking further.
Cook the butter until it turns golden. It will bubble up, so you need a spatula or spoon to scrape the bubbles back so you can see the colour. The butter will also start to smell nutty.
As soon as the butter starts to colour pour it straight into the bowl to stop it cooking.
Allow to cool completely.
Sift the sugar, almonds, flour and salt into a bowl.
Whisk in the egg whites and elderflower cordial until combined.
Finally add the cooled beurre noisette and whisk until it is fully mixed in.
The mixture can then be placed in the fridge overnight or for at least 8-10 hours. This helps the mixture thicken to the right consistency for baking.
Just before baking pre-heat the oven to 170 degrees (325 degrees F), Gas 3.
Take the madeleine pan and rub butter into the scalloped moulds, then dust the tray with flour. Tap off the excess flour and then fill each mould with a heaped teaspoon of batter.
You will have batter left over, do not over fill the moulds, you can use this batter to make more madeleines after your first batch.
Bake the madeleines in the pre-heated oven for 12-15mins, you may need to rotate the pan half-way through baking to ensure they cook evenly.
Whilst the madeleines are baking, make the glaze, sift the icing sugar into a bowl and add a tablespoon of the elderflower cordial, mix until it forms a thin pouring consistency, you may need to add the rest of the cordial to get the desired consistency.
Allow to cool slightly and then remove the madeleines from the pan, place them on a cooling rack with a tray or some greaseproof paper underneath to catch the glaze, glaze them while they are still warm.
If you don't have a madeleine pan you can use a small tart tin or mini muffin moulds.