Preheat your oven to 375°F (190°C).

In a large skillet over medium heat, cook the Italian sausage until browned, about 5-7 minutes. Add unsalted butter, diced onions, and celery. Sauté until the vegetables are softened, approximately 3-4 minutes. Stir in herb stuffing mix and chicken broth until moist; set aside to cool slightly.

Lay the turkey breast flat, slice horizontally through the thickest part to create a pocket, then cover with plastic wrap. Gently pound to a uniform thickness of about ½ inch. Season both sides generously with kosher salt and black pepper.

Spread the sausage stuffing evenly over the turkey breast, leaving a small border around edges. Roll turkey tightly into a log shape. Secure with kitchen twine.

In a small bowl, mix remaining softened butter with a pinch of salt and pepper. Rub half of the mixture over the exterior of the turkey roulade. Place seam-side down in a greased baking pan.

Bake for 55-60 minutes. Use a meat thermometer to check for 165°F (74°C). Increase oven temperature to 400°F (200°C) and drizzle remaining butter over roulade 20 minutes before done.

Let the roulade rest for 15 minutes after baking to allow juices to redistribute. Slice and serve alongside your favorite sides.