Bring a large pot of salted water to a rolling boil. Add trimmed brussels sprouts and boil for 10 to 12 minutes until tender when pierced with a fork. Drain completely in a colander and pat thoroughly dry with clean kitchen towels.

Preheat your oven to 425°F (220°C) and line a large rimmed baking sheet with parchment paper. Place the par-boiled sprouts spaced evenly across the sheet.

Using the flat bottom of a heavy drinking glass or mason jar, gently but firmly press straight down on each sprout until flattened into a 1/2-inch disc with broken, craggy edges.

In a small bowl, whisk together the olive oil, melted butter, minced garlic, sea salt, black pepper, and red pepper flakes. Generously brush the seasoned garlic butter over both sides of each smashed sprout.

Sprinkle half of the grated Parmigiano-Reggiano over the sprouts. Roast at 425°F (220°C) for 20 to 25 minutes until deeply golden brown and crackling crisp around the edges. Shower with remaining parmesan during the last 3 minutes of baking.

Transfer to a serving platter, drizzle with glossy balsamic glaze, and garnish with fresh parsley. Serve immediately alongside the lemon garlic aioli!