1. Preheat oven to 160ºC.
2. Drizzle olive oil into an ovenproof baking dish; place sole filets on top.
3. Add fish stock and sprinkle with salt then cover.
4. Place in oven and bake for 10 to 15 minutes or until the filets are cooked.
5. Remove filets from the pan and keep warm. Reserve the stock and strain for the sauce.
6. In a large skillet, add half of the butter and melt over medium heat.
7. Add the mushrooms and sauté for a couple minutes; season with salt and pepper. Stir and remove mushrooms from the skillet.
8. In the same skillet, melt the remaining butter over medium-high heat.
9. Add the shallots and flour, whisk together and cook for 1 minute.
10. Add the reserved stock, white wine and Aged Havarti cheese; continue whisking and bring to a slow boil.
11. When the sauce has boiled for 5 minutes, add the mushrooms and season with salt and black pepper.
12. Meanwhile, in a small saucepan of boiling salted water, blanch the peas; drain and set aside.
13. Place filets on a platter or individual serving plates and top with mushroom sauce.
14. Serve with fresh peas and chives.