Heat oven to 350 (180C) and spray or grease a 12-count muffin pan. Distribute the walnuts evenly among the pans.
Take a small saucepan and over a low heat slowly melt the butter and chocolate, stir together until smooth. Gently stir in the brown sugar and set aside to cool for about 10 minutes.
When the mix still just warm stir in the egg then sift in the flour and add the sour cream and stir until combined.
Spoon the mixture over the walnuts into the muffin holes. Take 2 pieces of the Caramello chocolate and place on top of each muffin hole and push down gently to allow the brownie mixture spread so they are completely enclosed. Bake for 15-18 minutes. Remove from oven and using a small sharp-pointed knife, or small palette knife; loosen the sides of the brownies from the pan holes. Let them stand for 10 minutes before gently removing from pan.