2 large eggs
1 cup whole milk
1 cup all-purpose flour
1 tbsp. unsalted butter, melted
2 scallions, chopped
3/4 lb. Yukon Gold potatoes (about 2), peeled, and cut into the 1/4-inch dice
1 (12 ounce) packaged bulk sausage meat
2 tbsp. vegetable oil
1/2 cup grated Parmesan cheese
1. Adjust oven rack to upper-middle position and heat over to 425 degrees F. Prepare a 9-inch springform pan by lining the bottom of the pan with aluminium foil (preferably nonstick), attaching the sides of the pan, and tucking the foil underneath the pan bottom. Coat the sides and bottom with cooking spray. Set the pan aside on a rimmed baking sheet.
2. Whisk eggs, milk, and 1/2 tsp salt in bowl until well combined. Stir in flour until just incorporated; the mixture will be a bit lumpy. Whisk in butter until batter is smooth. Stir in scallions and set batter aside while preparing filling.
3. Toss potatoes with 1 tbsp. water in large microwave-safe bowl. Cover with plastic wrap, cut vent holes in plastic, and microwave on high power until potatoes just begin to soften, 3-4 minutes. Meanwhile, cook sausage in large nonstick skillet over medium heat, breaking up clumps, until meat has lost most of its pink coor, about 4 minutes. Using slotted spoon, spread sausage evenly over bottom of prepared springform pan.
4. Heat oil in skillet with sausage fat over medium-high heat until shimmering. Add potatoes and 1/4 tsp salt and cook until potatoes are golden and crisp, 8-10 minutes. Drain potatoes on paper towels.
5. While potatoes are cooking, place springform pan with sausage in over for 10 minutes. Remove pan from oven and, working quickly, sprinkle 1/4 cup cheese over sausage and pour bater evenly over filling. Scatter potatoes on top and sprinkle with remaining cheese. Bake until puffed and golden, 25 to 30 minutes. Remove pan from oven, run knife around edges of pan, and let cool for 5 minutes. Release outer ring and, using spatula, transfer casserole to serving plate. Serve warm.