Preheat the oven to 425°F. Prepare an 18"x13" rimmed sheet pan by spraying with nonstick cooking spray, and set a second rimmed sheet pan (same size) aside.
In a large skillet, over medium-high heat, heat the olive oil. Add the hash browns, garlic powder, onion powder, kosher salt, and black pepper. Cook for 10-12 minutes, stirring occasionally, until the potatoes are tender and golden brown. Transfer the potatoes to a large bowl and set aside.
2 tablespoons olive oil, 4 cups hash brown potatoes, ½ teaspoon garlic powder, ½ teaspoon onion powder, ½ teaspoon kosher salt, ¼ teaspoon black pepper
Add the breakfast sausage to the same skillet. Cook for 6-8 minutes, breaking the sausage into crumbles, until browned and cooked through. Drain any excess grease, and then add the sausage to the bowl with the potatoes.
16 ounces ground breakfast sausage
In a mixing bowl, whisk together the large, whole milk, and kosher salt.
8 large eggs, 1/4 cup milk, ½ teaspoon kosher salt
Melt 1 tablespoon butter, in the same skillet pan, over medium low heat. Add the egg mixture and cook for 3-4 minutes, gently stirring with a spatula, until the eggs are softly scrambled and still slightly glossy. Remove the skillet from the heat.
1 tablespoon butter
Arrange 6 of the flour tortillas around the edges of the prepared sheet pan (the one with cooking spray), overlapping them slightly and allowing about half of each tortilla to hang over the sides of the sheet pan.
1 package (8 ct) burrito-size flour tortillas
Sprinkle half of the shredded cheese evenly over the tortillas. Spread the cooked hash brown potatoes and crumbled sausage over the cheese, then spoon the scrambled eggs evenly over top. Sprinkle the remaining cheese over the eggs.
1 block (16 oz) Colby Jack cheese
Place the remaining 2 tortillas across the center of the filling to completely cover the top. Fold the overhanging tortillas inward over the filling, overlapping them as needed to cover the top completely. * If you're having trouble getting the flour tortillas to stay (the ones that you folded over to close in the quesadilla, you can use toothpicks to secure the tortillas together. Just remember to take them out after baking! Or leave them in for a few minutes to get them to stay in place, and then remove them before baking. Melt 2 tablespoons of butter in a microwave-safe bowl, and then brush it evenly over the tortillas.
2 tablespoons butter
Turn the second sheet pan upside down and spray the bottom of it with cooking spray. Place the sheet pan directly on top of the quesadilla, make sure the flat bottom that you sprayed with cooking spray is touching the quesadilla, and gently press it down.
Bake for 20 minutes. Carefully remove the top sheet pan using oven mitts, and then continue cooking for 5-8 minutes until the tortillas are crisp and golden brown.
Remove the quesadilla from the oven and let it sit and rest for 10 minutes. Cut into squares and serve warm. Enjoy!