Salmon thawed. Clean and wash spring onions and cut into thin rings. Rinse salmon and dab dry. Season with salt and pepper. Put the salmon in a greased casserole dish. Sprinkle with the spring onions.
Preheat the oven (electric cooker: 175°C/circulating air: 150°C/ gas: level 2). Bring sour cream and cream to a boil in a pot. Carefully stir in the sparkling wine at low heat and stir until the carbon dioxide has escaped (Careful! The carbon dioxide causes the sauce to boil over quickly).
Season to taste with salt, pepper and stock.
Pour sauce over the salmon fillet. Cook in a hot oven for 20-25 minutes.
Meanwhile cook the rice in boiling salted water according to package instructions. Arrange everything and garnish with lemon.