Melt butter in a heavy-bottomed saucepan over medium heat. Add the onions and cook until translucent – approximately 3-5 minutes. Add the pancetta and sauté until lightly browned – approximately 1-2 minutes. Stir in rice. Sauté until the rice is light golden brown – approximately 3-4 minutes.
Add the warm stock to the rice a ladle at a time, stirring constantly and allowing stock to be absorbed between each addition. It should take about 20 minutes.
Once rice is tender and all liquid is absorbed, add salt, pepper, lemon juice, lemon zest, and pesto. Keep warm.
Whip cream to soft peaks with electric mixer. Garnish risotto with whipped cream and serve.