In a large pot, melt butter over medium heat. Add onion, leek, and carrot and cook until softened, about 5-7 minutes.

Add stock and potatoes to the pot. Bring to a boil, then reduce heat and simmer for 15-20 minutes, or until potatoes are tender.

Add burbot and bay leaf to the pot. Simmer for another 5-10 minutes, or until fish is cooked through.

Stir in cream and dill (if using). Remove bay leaf before serving.

For Rieska: Preheat oven to 400°F (200°C). In a bowl, combine flour, salt, and baking powder. Add milk and butter and mix until a soft dough forms.

Roll out the dough thinly on a floured surface. Cut into wedges or desired shapes. Place on a baking sheet and bake for 10-12 minutes, or until golden brown.

Serve the soup hot with warm Rieska.