1️⃣ Preheat & Prep:

• Preheat oven to 375°F (190°C).
• Grease a 9×13-inch baking dish and set aside.

2️⃣ Cook the Kielbasa & Onions:

• In a large skillet over medium heat, melt butter and cook sliced kielbasa for 3-4 minutes, until lightly browned.
• Add diced onion & minced garlic and cook for another 2 minutes until fragrant.

3️⃣ Prepare the Sauce:

• In a large bowl, mix together cream of mushroom soup, sour cream, Dijon mustard, salt, black pepper, smoked paprika, and milk until smooth.

4️⃣ Assemble the Casserole:

• Spread potatoes (or frozen hash browns) evenly in the prepared baking dish.
• Pour the soup mixture over the potatoes and stir to coat.
• Mix in the browned kielbasa & onions.
• Stir in 1 ½ cups shredded cheddar cheese and ½ cup mozzarella cheese (if using).

5️⃣ Add the Topping:

• If using, mix crushed crackers with melted butter and sprinkle over the casserole.
• Top with the remaining ½ cup shredded cheddar cheese.

6️⃣ Bake:

• Cover with foil and bake for 40 minutes.
• Remove foil and bake for another 10-15 minutes, until golden and bubbly.

7️⃣ Cool & Serve:

• Let rest for 5 minutes, garnish with chopped parsley, and serve warm!