6 cups chicken stock
1 tbsp. saffron threads
3 tbsp. unsalted butter
2 small yellow onions, minced
2 cups Arborio rice
1 cup dry white wine
2 oz. raw bone marrow (optional)
1⁄2 cup grated Parmesan
Kosher salt and freshly ground black pepper, to taste
Heat stock and saffron in a 2-qt. saucepan over medium heat; keep warm. Heat butter in a 4-qt. saucepan over medium-high heat. Add onions; cook until soft, about 4 minutes.
Add rice; cook until lightly toasted, about 4 minutes. Add wine; cook until evaporated, about 2 minutes. Add 1⁄2 cup warm stock; cook, stirring, until absorbed, about 2 minutes.
Continue adding stock, 1⁄2 cup at a time, and cooking until absorbed before adding more, until rice is tender and creamy, about 16 minutes total. Stir in marrow, if using, and Parmesan; season with salt and pepper.