Take milk out of the fridge and let it set for a couple of hours until tepid. Add the dried yeast to the milk, cover, and let it activate for about 15 minutes until frothy.
Pour the mixture into the bowl of a stand mixer and stir with a dough hook, adding in the melted butter. Add the sugar and stir again. Add half of the flour as well as the salt, baking powder and ground cardamom. Add half the beaten egg (reserve the other half for brushing before baking).
Mix well and start adding in more of the flour, bit by bit, until the dough becomes slightly sticky. Knead the dough for at least 5 minutes. Cover the bowl and let rise until doubled – about 30–40 minutes.
Turn the dough out to a floured surface and knead for a few minutes, adding more flour if needed. You want a firm but moist dough. Cut the dough into 12 equal-sized pieces and place on a baking sheet. Leave them rise again for 25–30 minutes.
Preheat the oven to 400°F.
Brush each bun with the other half of the beaten egg and bake for 8–10 minutes. Remove them from the oven and cover the buns with a slightly damp dish towel immediately – this will prevent them from forming a crust.
When they have cooled completely, cut a ‘lid’ off the buns – 1 inch from the top. Add about 2 tsp jam on the bottom of the buns.
Whip your cream with sugar and vanilla (if using) until stiff, then dollop cream on top of the jam. Put the ‘lids’ back on and dust them lightly with powdered sugar before serving.