Leek onions clean, wash and in approx. 1/2 cm broad little rolls cut. Grate cheese roughly. Chop walnuts coarsely. Whisk buttermilk and eggs. Mix flour, baking powder, soda, cheese, nuts and salt in a mixing bowl.
Cut 250 g butter into cubes and add to the flour mixture. Mix quickly with your fingertips to a coarse crumbly dough. Stir in the buttermilk and egg mixture and spring onions briefly. Stir only until just enough to form a dough.
Pour the dough onto a floured work surface and shape into a round scone about 2.5 cm high. Put it on a baking tray lined with baking paper. Cut with a knife in such a way that 8 indicated "cake pieces" are formed.
Scone in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 20-25 minutes until golden brown.
Remove the scone from the oven and let it cool on a cake rack for at least 10 minutes. Serve with ham and remaining butter.