Preheat oven to 400°F (200°C).

Cream together the softened butter and sugar until light and fluffy.

In a separate bowl, lightly beat the egg.

Add the beaten egg to the butter and sugar mixture and mix well.

Pour in the milk and stir to combine.

In a separate bowl, sift together the flour, baking powder, crushed cardamom seeds, and salt.

Gradually add the dry ingredients to the wet ingredients, stirring as little as possible until just combined.

Turn the dough out onto a lightly floured board.

Shape the dough into small, round buns.

Place the buns on a baking sheet lined with parchment paper.

Bake in the preheated oven for about 10 minutes, or until lightly golden.

Remove the buns from the oven and let them cool slightly.

Cut each bun in half horizontally.

Return the cut buns to the baking sheet, cut-side up.

Reduce the oven temperature to 300°F (150°C).

Bake in the slow oven until the rusks are dry and golden brown, about 15 minutes.