dough:

1 portion of basic sweet yeast dough
2 tsp vanilla sugar
1 egg for glazing

butter
sugar

Prepare a basic sweet yeast dough according to the instructions given here, with the addition of vanilla sugar.

After the dough has risen, knead it lightly and form into small buns. Place the buns on a baking sheet covered with parchment paper, cover with towel and let rise until the buns are doubled in size.

Meanwhile, cut the cold butter in small chunks, about 4 cm long and 1 × 1 cm wide. Gently press a deep hole  —  an "eye"  —  in every bun with your finger. Place a chunk of butter upright in every hole, brush the buns with lightly beaten egg and pour lots of sugar over the butter into the holes to fill them. In these buns, there cannot be *too much* butter or sugar as filling.

Bake the buns at 225 °C for 8 - 10 minutes. Serve them warm with coffee, tea or a cup of cocoa.
Makes about 20 buns.

Recipe source: family recipe/traditional Finnish recipe.