Sturgeon Fillets Baked in Sauerkraut and Wild Mushrooms

Name: Sturgeon Fillets Baked in Sauerkraut and Wild Mushrooms
Ingredients: 3 oz (80-85 g) dried wild mushrooms (e.g. porcini); or 9 oz (250 g) fresh ones.; 2 garlic cloves; 9 oz (250-255 g) sauerkraut; ½ leek (just the white part); 4 sturgeon fillets (small-ish; roughly 9 oz / 250 g each); coarsely ground black pepper, to season; 3 - 4 tbsp flour; olive oil, for frying; 1 tbsp wholegrain mustard; 2 tbsp raisins; 2 tbsp wine vinegar; 1 tbsp honey; salt, for seasoning; 1 lemon, optional, for garnish