Preheat oven to 300°F.

Spray 12-cup muffin tin with nonstick cooking spray; set pan aside.

Using a large bowl, add bread cubes and butter; toss until well coated.

Spread bread cubes evenly onto a rimmed baking sheet. Bake for 12 minutes, or until lightly toasted.

Remove bread cubes from oven and place in a large bowl.

Increase oven temperature to 350°F.

Meanwhile, place sausage in a medium skillet and cook over medium heat for 5-7 minutes, or until fully cooked. Transfer cooked sausage into bowl with the bread cubes.

Using the same skillet, add onions and celery; sauté, stirring occasionally, for 5-7 minutes, or until softened.

Add garlic, sage, rosemary, salt and pepper; stir until well combined. Continue sauteing, stirring often, for 1-2 more minutes.

Transfer onion mixture into bowl with the bread cubes; stir until well combined.

Divide mixture evenly into the cups of the muffin tin. Press the stuffing down firmly into each of the cups. (Tip: I just used my hands for this step. It’s messy, but much easier!)

Bake at 350°F for 26-28 minutes, or until tops are golden brown and internal temperature is at least 160°F.

Let cool in pan for 5 minutes and then run a thin spatula or knife around each muffin cup to loosen the muffins.

Transfer to a wire rack. Serve warm.