Preheat the oven to 150'C.
Pass the almonds and icing sugar through a medium sieve to remove any lumps.
Whisk the egg whites with 150g of caster sugar. Whisk until you have a semi-stiff and glossy meringue.
Stir in one third of the dry ingredients. Once incorporated, repeat with the second third and then the final third. Add the food colouring and work the mixture with a spatula until it is smooth, shiny and a dropping consistency.
Fill a piping bag with the macaroon mix and pipe the macaroons onto a lined baking tray. Tap the tray on your work surface to smooth out the tops and remove any large air bubbles. Leave the macaroons to dry for 15 minutes at room temperature. They are ready to cook when the surface is touch-dry. Transfer to the oven and bake for 10-12 minutes. The macaroons are cooked when the top is firm. Remove from the oven and leave to cool for 10 minutes. After 10 minutes, lift the macaroons from the baking parchment and turn them over. Allow to cool thoroughly before filling.
Remove the skin and muscle from the foie gras and chop into pieces. Place the foie gras and butter (at room temperature) into a food processor and mix until smooth and even.
Whip the cream and add it to the foie gras. Mix together until you obtain a smooth mousse and then add the port and mix through.
When the macaroons have cooled down, fill half of the shells with the foie gras mousse and place the other halves on top.
«Allow the piped macaroons to rest at room temperature for 10-15 minutes before baking.»