Preheat oven to 350°F. Lightly grease an 8x8 baking dish.
Add the quartered donuts to the pan, spreading them evenly.
In a bowl, whisk together the heavy cream, milk, eggs, sugars, melted butter, vanilla, cinnamon, nutmeg, and salt.
Pour the custard evenly over the donuts and gently press them down so they soak.
Let rest for 15 minutes to fully absorb.
Bake uncovered for 30–35 minutes, until the center is just set and the top is golden.
Rest for 5–10 minutes before glazing.