Preheat oven to 375 °F (190 °C) and lightly grease a 9×13-inch baking dish with nonstick spray.
Peel and thinly slice the potatoes, then arrange them evenly in the baking dish.
Cook bacon in a skillet until crispy, then drain on paper towels and reserve 1 tablespoon of bacon grease in the skillet.
Add ground sausage, diced onion, and minced garlic to the skillet; cook until the sausage is browned and fully cooked.
Sprinkle flour over the sausage mixture, stir and cook for 1–2 minutes.
Gradually whisk in chicken broth and then heavy cream; simmer for 3–5 minutes until the sauce slightly thickens.
Crumble the cooked bacon and sprinkle it along with the chopped kale evenly over the potatoes.
Pour the sausage and cream mixture evenly over the potatoes and gently spread to coat all ingredients.
Top with shredded Parmesan cheese, cover tightly with foil, and bake for 50 minutes.
Remove foil and bake an additional 10 minutes until potatoes are tender and the top is golden.
Allow the casserole to rest for 5–10 minutes before serving.