Step 1

Preheat the oven to 350 degrees F.

Step 2

Lightly grease a 9x13-inch baking dish.

Step 3

In a large skillet over medium heat, add the sausage and the onion and cook, while crumbling the meat, until the sausage is no longer pink and the onion is translucent, about 6-8 minutes.

Step 4

Transfer the sausage-onion mixture to a paper-towel-lined plate to drain. Carefully wipe the skillet clean.

Step 5

Reduce the heat to low and add 1/4 cup of the butter to the skillet. Cook, whisking often, until melted.

Step 6

Whisk the flour into the butter until smooth. Cook, whisking constantly, about 1 minute.

Step 7

Gradually whisk the milk into the butter mixture.

Step 8

Increase the heat to medium and cook the milk mixture, whisking constantly, until it thickens and is bubbly, about 5-6 minutes.

Step 9

Whisk the shredded cheese into the milk mixture and cook, whisking often, until the cheese is melted and the mixture is smooth, about 30-40 seconds.

Step 10

Stir the sausage mixture, the salt, and the pepper into the cheese sauce.

Step 11

Pour the sausage mixture into the prepared baking dish.

Step 12

Arrange the crescent roll dough on top of the sausage mixture.

Step 13

Bake the casserole until the top is golden-brown and the sausage mixture is bubbly, about 30-35 minutes.

Step 14

Microwave the remaining butter in a small microwaveable bowl on high heat until melted, about 20 seconds.

Step 15

Transfer the casserole from the oven. Brush the top with the melted butter and sprinkle with the chives.

Step 16

Let the casserole stand for 10 minutes.

Step 17

Serve.