Butternut Squash Risotto

2 tablespoons unsalted butter
1 sprig fresh sage
2 cups chopped peeled butternut squash
1 small onion, coarsely chopped
3 large cloves garlic, smashed
Kosher salt
1 1/2 cups arborio rice
1/4 cup dry white wine
2 cups low-sodium chicken broth
1 2-to-3-inch parmesan cheese rind (optional)
1 cup coarsely chopped aged gouda cheese, plus shaved gouda for garnish
Freshly ground pepper
2 cups arugula