Gnocchi

1-pound red-skinned sweet potatoes (yams), rinsed, patted dry, pierced all over with fork
6-ounces fresh ricotta cheese
1/2 cup finely grated Parmesan cheese
1 tablespoons (packed) golden brown sugar
1 teaspoons plus 1 tablespoons salt
1/4 teaspoon freshly ground nutmeg
1 3/4 cups (about) all purpose flour

Sauce (makes 2 cups)

2 cups milk, heated,
1/4 onion
2 cloves garlic
3 sage leaves
Salt and freshly ground white pepper, to taste
3 Tbs. unsalted butter
3 Tbs. all-purpose flour
1 cup Gouda cheese, shredded