Add 1 tablespoon butter and 1 tablespoon olive oil to the pancetta fat. Stir in 1 diced shallot and 2 minced garlic cloves. Cook until softened and fragrant, about 2 minutes.
Stir in 1 ½ cups arborio rice and cook for 1–2 minutes, coating each grain in the fat. Pour in ½ cup white wine and stir until mostly absorbed.
Using a ladle, add 1 cup of warm stock at a time, stirring frequently and waiting for the liquid to be absorbed before adding more. Continue until the rice is creamy and al dente, 18–20 minutes (you may not need all the stock).
Stir in 4 cups chopped kale, 1 teaspoon salt, and ½ teaspoon black pepper. Cook until the kale is tender and wilted, about 3 minutes.
Remove from heat and stir in 1 cup grated Parmigiano Reggiano, the zest and juice of 1 lemon, and an extra tablespoon of butter if desired.
Spoon the risotto into bowls. Top each serving with crispy pancetta and toasted walnuts. Serve immediately.