Preheat the oven to 190°C. Grease and line two 11cm x 6cm cake tins.
Beat the butter and sow thistle petals in a heatproof bowl until well incorporated. Place the bowl of butter into the heating oven to melt as you prepare the rest of the batter.
Sift the icing sugar and flour into a large mixing bowl. Add the ground almonds. Set aside.
Beat the egg whites for 2 minutes. Fold the melted butter, beaten egg whites and vanilla into the almond mixture. Pour half of the cake batter into each of the lined cake tins. Drop half of the berries into the centre of each tin, then pour in the remaining cake batter.
Cook for 50 minutes until golden, or until a skewer comes out clean when tested.
Cool in the tins completely before tuning out.
Dust the cakes with icing sugar and decorate with wildflowers, if you wish.
If you’re going out foraging be 100% certain that what you’re picking is edible. When in doubt, don’t pick it – or consult an expert.