Heat the olive oil and butter together in a wide saucepan. Add the finely chopped onion and garlic and cook gently for five to six minutes until soft and translucent, with no colour. Meanwhile, blitz half of the peas with a small splash of the hot stock until completely smooth, then set aside.

Stir the arborio rice into the pan and cook for a couple of minutes until the grains are glossy and lightly toasted. Begin adding the hot stock a ladle at a time, stirring regularly and allowing each addition to be absorbed before adding the next. When roughly half the stock has been used, stir in the pea purée, the remaining whole peas and the lemon zest. Continue adding stock gradually until the rice is just tender and the risotto is loose and creamy.

Remove from the heat and stir through half the grated parmesan, seasoning to taste. Finish with the shredded mint and serve immediately with the remaining parmesan sprinkled over the top.