Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Line a baking tray with baking paper. Mix 450 g flour, baking powder, baking soda, 1 pinch of salt, sugar and citrus peels in a bowl.
Add butter in pieces. Quickly rub with your hands to form crumbles.
Whisk eggs and buttermilk. Add to the crumbles. Mix in briefly with a fork until a crumbly dough is just formed. Halve the dough. Shape each into a square (approx. 20 x 20 cm) with floured hands on some flour.
Spread jam in a square. Place the remaining square of dough on top. Cut into about 16 cubes with a floured knife. Place them on the baking tray with some distance between them. Bake in a hot oven for about 20 minutes.
Take out the scones. Serve still warm with some jam or clotted cream.