In a large bowl, combine whole milk, sifted all-purpose flour, granulated sugar, instant yeast, ground cardamom, and salt until well mixed to create the dough base.

Add eggs and small pieces of lightly salted butter to the mixture and knead for 5-7 minutes until the dough becomes smooth and elastic.

Cover the dough with a clean kitchen towel and place it in a warm area to rise until doubled in size, approximately 1 hour.

While the dough rises, cream room temperature butter and brown sugar using a mixer until fluffy, then gently fold in chopped frozen raspberries to create the filling.

Roll out the risen dough on a floured surface into a half-inch thick rectangle. Evenly spread the raspberry filling over the surface.

Carefully roll the dough into a tight log shape. Cut the log into 12 equal pieces and arrange them cut-side up in a greased baking dish.

Cover the arranged buns and allow them to rise again for about 30 minutes until puffed.

Heat the oven to 375°F (190°C) to prepare for baking.

Bake the buns for 20-25 minutes until golden brown on top.

In a saucepan, whisk egg yolks, granulated sugar, and cornstarch. Gradually add whole milk and vanilla. Cook over medium heat, stirring continuously until thickened.

Remove custard from heat and let cool slightly. Serve warm raspberry custard buns alongside the creamy custard.