Heat chicken stock over medium heat until hot, not boiling.
Heat butter and olive oil in a dutch oven or large fry pan over medium to high heat until butter is melted.
Add onion, and fry off stirring occasionally until translucent - about 5 minutes.
Add rice, and stir coating every single grain of rice in the butter and oil - about 5 minutes.
Add white wine, and stir the bottom of the pan to release juices.
Reduce heat to low - medium, and add chicken stock, a ¼ of a cup at a time. Do not stir the risotto. In between each addition of stock, simmer risotto without letting it stick to the pan. Risotto should be simmering gently, but not absorb all the stock. Keep adding stock, bit by bit until rice starts to become tender and the stock is all used up.
Add mushrooms, peas, lemon zest and juice. Stir to combine. Let simmer for an additional 5 minutes, then add parmesan cheese and stir.
Serve with fresh herbs and extra parmesan cheese.