Melt 2 tbsp. butter in a large skillet over medium-high.

Cook onion until golden, 6–8 minutes; add garlic until fragrant; transfer to a bowl.

Add remaining butter and ground veal to skillet; cook, breaking up meat into small pieces, until browned, 6–8 minutes; transfer to bowl with onion mixture.

Add spinach to the skillet; cook until wilted, 1–2 minutes; transfer to a colander to drain. Squeeze spinach dry, roughly chop, and add to bowl with veal and onion mixture.

Stir filling mixture while adding nutmeg, salt, and pepper.

Melt 2 tbsp. butter in a medium size saucepan, over medium heat.

Add garlic to saucepan and cook until golden, 1–2 minutes.

Add crushed tomatoes, salt and pepper; cook until thickened, 8–10 minutes, and let cool.

Purée milk and eggs in a blender until smooth.

Add cooled tomato sauce mixture, salt and pepper; pulse 2 to 3 times until just combined.

Cook Lasagna sheets, fresh or dried, as directed on package.

Heat oven to 375°.

Grease a 9”x13” deep baking dish with butter.

Lay 2 lasagna sheets in prepared dish, overlapping slightly.

Sprinkle 1 1⁄2 cups filling over top and drizzle with 1 cup sauce; sprinkle with 1⁄2 cup Toma, about 5 oz. mozzarella, and dot with 1 tbsp. chilled butter.

Repeat layering lasagna sheets, filling, sauce, cheeses, and butter.

Cover lasagna with greased parchment paper or aluminum foil;

Bake until filling is set, about 45 minutes.

Heat oven broiler. Uncover lasagna; broil until cheese is browned, 2–3 minutes.