Heat the olive oil and butter together in a wide pan over medium heat until shimmering and fragrant.
Add the finely chopped onion and cook, stirring often, until translucent and soft, about 5 minutes. The onion should smell sweet and look slightly glossy.
Stir in the arborio rice, cooking for 1-2 minutes until the grains are well coated and start to look slightly translucent at the edges with a faint toasty aroma filling the air.
Pour in a ladleful of hot vegetable broth, stirring constantly until mostly absorbed. Continue adding broth, one ladle at a time, allowing each addition to be absorbed before adding the next, maintaining a gentle simmer.
After about 15 minutes, when the rice is tender but still has a slight bite and the mixture is creamy, start preparing the peas.
Meanwhile, blanch the green peas in boiling water for 1 minute until bright green and tender. Drain and set aside.
Gently fold in the blanched peas, grated Parmesan, and a small knob of butter, stirring until the cheese melts and peas are evenly distributed, creating a vibrant, fragrant mixture.
Remove from heat and let sit for 2 minutes, allowing the flavors to meld and the risotto to settle into a luscious, velvety consistency.
Serve immediately, garnished with extra Parmesan if desired, and enjoy the bright, comforting flavors of this spring-inspired risotto.
