Wash the leeks well and slice. Wipe the mushrooms and slice.
Heat the olive oil in a saute pan. Add the leeks and mushrooms, cooking over medium heat for about 5 minutes or until softened. Add the garlic and cook another minute. Remove vegetables from pan and set aside.
Add 2 tablespoons of the butter to the pan and saute the onion over medium heat for approximately 5 minutes.
Stir in the arborio rice and cook for 1 minute. Add one cupful of fresh stock to the pan and cook gently, stirring occasionally; until all liquid is absorbed.
Continue stirring in one cupful of stock at a time, until each cupful is absorbed. This should take about 25 minutes. The risotto should by the end turn thick and creamy; the rice tender but not sticky.
Just before serving, stir in the leeks and mushrooms, the remaining 2 tablespoons of butter, lemon juice and zest, half of the cheese, and the fresh herbs.
Adjust seasoning, adding salt and pepper to taste. Sprinkle remaining cheese on top, garnish with herb sprigs and lemon wedges. Serve warm.