Clotted cream shortbread is a delicacy that I always buy myself when in Cornwall and I thought I'd give it a go at home, since we will not be going to Cornwall until next year. I couldn't find a recipe anywhere, but using the proportions of butter/clotted cream specified on the outside of the last packet that I ate, I managed to adapt my own shortbread recipe. The clotted cream flavour was quite subtle, even when I remade it with a greater quantity of clotted cream, but the biscuits themselves were much lighter than usual.
2oz butter (softened)
2oz clotted cream
2 oz caster sugar
6oz plain flour
Preheat oven to 180C. Mix together butter and clotted cream and mix in the sugar. Then rub in the flour and bring it together to form a dough. It's up to you what you do at this stage - you could press it into a tin or make shapes as I did. If making shapes, it's best to chill them in the fridge for 30 minutes before baking otherwise they tend to overswell. Bake for 20 minutes or so until starting to turn golden.