Heat a large skillet over medium-high heat and brown the sausage.
Add the onion, garlic, and sage and cook until translucent, and transfer to a large mixing bowl and allow to cool.
Beat together the eggs and half and half and add to the sausage mixture.
Add the fontina and Parmesan to the bowl and stir to combine.
Add the toasted croissant cubes and fold together to combine.
Place the mixture in a baking dish and refrigerate for at least 2 hours or overnight.
When you’re ready to cook the bread pudding, preheat the oven to 350°F and bake for 35 minutes, or until set and golden brown.
Garnish with the green onions and serve immediately.