Preheat the oven to gas mark 4/350oF/180oC and line a 12-count muffin tin with 12 muffin cases.
In a large bowl, add the, self-raising flour, baking powder, ground pistachio and salt. Mix together and set aside.
In a large mixing bowl, cream together the butter and caster sugar until light and fluffy. Then mix in the vegetable oil.
Add the 2 eggs and vanilla extract then combine. Add in the sour cream and milk and combine then mix in the green food colouring if using.
Pour the dry ingredients into the wet ingredients and combine all the ingredients together. Once all the ingredients are mixed, spoon the mixture into the muffin cases. The cases should be filled close to the top.
Bake for 20 – 25 minutes or until a cake tester comes out clean. Once you remove them from the oven, allow to cool in the tin for 15 minutes then transfer the muffins to a wire rack to completely cool.