Preheat the oven to 180°C (360 F).

Place the hazelnuts on a baking tray and toast in the middle of the oven for about 10-15 minutes, or until lightly coloured and the skins are blistered.

Remove the hazelnuts from the tray and place on a kitchen towel to stop the roasting and let cool. Close the kitchen towel and rub the hazelnuts to remove the skins. Transfer the hazelnuts to a food processor and grind them into a powder.

Melt the butter over a medium heat while continuously stirring. Once melted, continue to cook the butter for a further 3-4 minutes: it will start to bubble and foam. Continue to stir. At this point, the butter will begin to change to a light brown colour. At the same time, you will start to smell a nutty aroma. As soon as you do, take the pan off the heat and transfer the browned butter to another bowl to stop the butter from cooking.

Sift the icing sugar, ground hazelnuts and flour into a mixer bowl.

Add the egg whites, vanilla extract and vanilla seeds. Mix on a medium speed until homogenous. While still mixing, add the still hot brown butter into the batter and mix until combined. Chill the batter overnight in the refrigerator.

The next day, preheat the oven to 170°C (338F).

Pour the financiers batter until into financiers moulds (or mini cupcake pans) until about 3/4 full. Cook for between 10-15 minutes depending on the size of the mould. The financiers should no longer be wet, and should feel springy to the touch, and look puffed up and golden.

Remove from the oven and leave to cool. Once cool, remove the financiers from their tins.