Layerless Sheetpan Lasagna

Ingredients

• 3 tablespoons olive oil, divided
• 3 tablespoons butter, divided
• 1 pound Italian sausage
• 1 pound lasagna noodles broken into pieces, reserve 1 cup pasta water (I actually used bow tie since I had it on hand)
• 3 cloves garlic, minced
• 1 small purple onion, minced
• 1 cup ricotta cheese
• 1 teaspoon Italian seasoning
• 1/2 teaspoon kosher salt
• 1/2 teaspoon red pepper flakes
• 4 cups marinara sauce (from your favorite jar)
• 2 cups shredded Italian cheese
• 1 cup Parmesan