For the dough mix 375 g flour, baking powder and 1 teaspoon each of salt and sugar in a bowl. Add butter in pieces and 200 ml buttermilk. Quickly knead into a dough with the dough hooks of the mixer (it is still a little crumbly).
Cover and chill for about 15 minutes.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Line baking tray with baking paper. Coarsely grate cheddar. Clean and wash spring onions and cut into fine rings. Cut ham into strips.
Quickly knead the prepared ingredients, except for 2 tablespoons of cheese, into the dough.
Form a circle (approx. 22 cm Ø) on a floured work surface and cut into 8 cake pieces. Put the pieces back together on the baking tray to form a circle. Spread with 2 tbsp. buttermilk and sprinkle with remaining cheese.
Bake in a hot oven for 35-40 minutes.
For the mustard sour cream, mix sour cream, crème fraîche and the two types of mustard. Season to taste with salt and pepper. Wash the chives, shake dry and cut into small rolls. Take the scone out of the oven.
Separate the dough pieces again immediately with a knife, let them cool down a little. Sprinkle with chives. Add the mustard sour cream.