Sauté Mushrooms: Heat 1 to 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the sliced mushrooms and cook, stirring occasionally, until they are golden brown and have released their moisture. Season lightly with salt and pepper. Once browned, remove the mushrooms from the pan and set aside.
Cook Leeks and Garlic: In the same pan, add a little more olive oil if needed. Toss in the sliced leek and sauté for about 3 minutes until softened. Then add the chopped garlic and cook together for another 1 to 2 minutes until fragrant, being careful not to burn the garlic.
Toast the Rice: Reduce the heat to medium. Add the arborio rice to the pan and stir well to coat the grains with the oil and aromatics. Toast the rice gently for about 2 to 3 minutes, stirring frequently, until the edges become slightly translucent.
Deglaze with White Wine: Pour in the white wine, stirring continuously. Allow the wine to simmer until nearly all the liquid evaporates, which will intensify the flavors and prepare the rice for the stock.
Gradually Add Vegetable Broth: Ladle in about one cup of the hot vegetable broth. Stir the rice gently and let it simmer, allowing the rice to absorb the liquid slowly. Once most of the broth is absorbed, add another ladle of broth. Repeat this process, stirring regularly, until the rice is tender but still has a slight bite (al dente), approximately 18 to 20 minutes. If you run out of broth before the rice is done, feel free to add extra hot water or broth.
Finish with Cheese, Peas, and Mushrooms: Once the rice is nearly cooked, stir in the grated parmesan cheese and mix in a bit more broth to keep the risotto creamy. Add the frozen peas and the sautéed mushrooms. Cook for another minute or two until the peas are heated through.
Season and Serve: Taste and adjust seasoning with salt, freshly ground black pepper, and red pepper flakes if using. Serve immediately with extra parmesan on the side.