Add a little water to a skillet and cook sausage crumbling up the sausage with a spatula while it sautés, about 8 - 10 minutes. Remove from heat and let cool.
Whisk the eggs, milk, and spices in a large mixing bowl.
Add the shredded potatoes, shredded cheese, and cooked sausage. Stir. Then fold in the spinach. Mix until combined. Transfer to casserole dish. Melt 2 tablespoons of butter in the skillet and then mix in 1 cup panko bread crumbs until the butter is thoroughly absorbed. Sprinkle the mixture evenly over the casserole. Dot the top with the remaining 1 tablespoon of butter, cut into small pieces. Cover and bake for 30 minutes. Remove cover and bake an additional 20 - 25 minutes until golden brown on top. Let stand for 10 minutes to allow moisture to be absorbed. Cut into slices and serve.