Place the flour, baking powder, bicarb of soda and sugar in the stand mixer fitted with the paddle attachment. Briefly mix to combine the ingredients.
Add the cubed butter and mix until the butter had broken up and incorporated in to the flour.
Mix the cream and crème fraiche together and add to the mixer. Mix until combined.
Turn the dough out and press together with the heel of your hand. Divide the dough in 2 and place each one between two layers of cling film. Shape in to a 6 by 9 inch block flattening the surface with a rolling pin and ensuring the side are straight.
Wrap in cling film and place in the freeze for 30 mins or until firm.
Divide in to 10 triangles or squares, cover and freeze for 2 hours or overnight.
When ready to bake, brush each with double cream, sprinkle with nibbed sugar and bake at 170C for 15-18 mins until golden brown.
Allow to cool.
Add strawberry jam and Cornish Clotted Cream for a classic Cornish Cream Tea.