Heat a large skillet over medium-high heat. Remove casings from sausage if using links. Add sausage to hot, dry skillet and break into bite-sized crumbles. Cook for 6-8 minutes, stirring occasionally, until browned all over with no pink remaining. Transfer cooked sausage to a plate using a slotted spoon, leaving rendered fat in skillet.

Reduce heat to medium. Add butter to the skillet with the sausage fat. Once melted, add minced garlic and stir constantly for 1 minute until fragrant and lightly golden. Watch carefully to prevent burning.

Pour in heavy cream and bring to a gentle simmer. Cook for 2-3 minutes, stirring occasionally, until slightly thickened enough to coat the back of a spoon.

Add baby spinach in large handfuls, stirring continuously for 2-3 minutes until all spinach wilts down and turns bright green.

Return browned sausage to the skillet, stirring to combine. Let warm through for 1 minute.

While making the sauce, bring a large pot of salted water to a boil. Add fresh cheese tortellini and cook according to package instructions, about 3-4 minutes, until they float and are tender. Drain well in a colander, shaking off excess water.

Add drained tortellini to the skillet with the creamy sausage mixture. Gently fold together, being careful not to break the tortellini, until everything is coated in sauce.

Reduce heat to low. Add shredded mozzarella and grated Parmesan cheese. Stir gently until both cheeses melt completely and create a creamy, smooth sauce.

Season with salt and black pepper to taste. Add crushed red pepper flakes if desired. Remove from heat and garnish with chopped fresh parsley. Serve immediately while hot.