Preheat the oven to 375°F. Line a baking sheet with parchment paper. Set aside.
In a large skillet over medium-high heat cook the sausage and chopped onion together until no pin remains. Drain any excess fat from the pan.
Add ½ teaspoon dry Italian seasoning and baby spinach to the pan, Cook stirring until the spinach has wilted. Season to your taste with garlic salt and black pepper. Continue to cook for a couple of minutes until the juice released from the spinach has dried. Remove from the heat and set aside.
Press the crescent dough into a 12 x 16-inch rectangle. Sprinkle ½ of the shredded cheese down the center of the dough.
Spoon the Italian sausage and spinach mixture over the cheese, then cover with the remaining shredded cheese.
Make 1-inch cuts on each side of the filling at an angle starting at the edge of the dough. Fold the slices over each other.
Brush the top and sides with melted butter then sprinkle with grated Parmesan cheese and dry Italian seasoning.
Bake for 15-18 minutes until golden. Rest for 5 minutes on the pan then slice and serve.
Any creamy white cheese may be used in place of he Havarti.