• Melt butter in a large skillet over medium-high heat. Add potatoes in batches to brown on both sides. Season with salt and pepper as you brown and soften each batch. Transfer each browned batch to a large bowl.

  Add rosemary to the bowl of browned potatoes and toss to mix. Then set aside.
• In the same skillet, brown Italian sausage, and ground beef. Then transfer the browned meat to a paper towel-lined plate.
• Saute the chopped onions in the drippings from the sausage and beef. When the onions begin to soften, stir in the chopped mushrooms; cook about 5-7 minutes.

  Add garlic and stir until fragrant. Transfer the cooked veggies to the plate with the sausage and beef.
• Using the same skillet, melt 3 tablespoons butter over medium heat. Whisk in 3 tablespoons flour to form a roux. Add beef broth while whisking to form a smooth gravy. Stir in the cooked veggie mixture and meat into the gravy.
• Add in sour cream and stir until melted and well combined. Season with salt and pepper.

  Taste test; add additional seasonings as needed.

Pie Assembly

• Preheat oven to 375° F.
• Butter the inside and bottom of a deep springform 9-inch pan.
• Gently press 1 pie pastry into the bottom and sides of the pan, allowing the excess to hang over the edges.
• Layer in this order: bottom pie crust, meat mixture, Irish cheese, a layer of potatoes, meat mixture, Irish cheese, a layer of potatoes, meat mixture, slices of mozzarella, then the top pie pastry.

  The layers should create a mound-like shape. Tuck the top pastry gently into the sides of the outer pastry. Cut off excess from both crusts but leave enough pastry dough to roll up together and crimp along the edges, like a thick pie crust.
• Use a sharp knife to gently cut vent holes on the top pastry. Brush the top and crimped edges with the egg wash and sprinkle with paprika.
• Bake for 50 minutes. Remove from oven and cool on a cooling rack for about 10 minutes then release from the springform pan.