In a saucepan, heat olive oil and melt butter over medium heat.
Add chopped onion and minced garlic. Sauté until translucent.
Add sliced mushrooms and cook until they release their moisture and turn golden brown.
Stir in Arborio rice and cook for a couple of minutes until the edges turn translucent.
Gradually add vegetable broth, one ladleful at a time, while stirring constantly. Allow each ladleful to be absorbed before adding more.
Continue this process until the rice is creamy and cooked to an al dente texture.
Stir in frozen peas and cook for a few minutes until they are heated through.
Remove from heat and gently fold in ricotta cheese and grated Parmesan.
Season with salt and pepper according to taste.
Cover and let the risotto rest for a couple of minutes before serving.