1. Preheat the oven to 320ºF. Drizzle an ovenproof baking dish with olive oil; place sole filets on top.
2. Add fish stock and sprinkle with salt. Cover. Bake for 10-15 minutes or until the fish is cooked. Remove the fish from the pan and keep warm. Reserve the stock and strain for the sauce.
3. In a large skillet, add half the butter and melt over medium heat. Add the mushrooms and saute for a few minutes; season with salt and pepper. Stir and remove the mushrooms from the skillet.
4. In the same skillet, melt the remaining butter over medium-high heat. Add the shallots and flour, whisk together and cook for 1 minute.
5. Add the reserved stock, white wine and Aged Havarti cheese; continue whisking and bring to a slow boil. When the sauce has boiled for 5 minutes, add the mushrooms and season with salt and black pepper.
6. Meanwhile, in a small saucepan, blanch the peas in boiling salted water; drain and set aside.
7. Place the fillets on a platter or individual serving plates, top with mushroom sauce and serve with fresh peas and chives.