Prep the squash: Heat the oven to 400°F (200°C). Halve the spaghetti squash lengthwise and scoop out the seeds. Drizzle the cut sides with olive oil and season with salt and pepper. Place cut-side down on a lined baking sheet.

Roast: Bake for 35–45 minutes, until the skin yields slightly when pressed and the strands pull away easily with a fork. Don’t over-roast or it can get mushy. Let cool slightly, then use a fork to scrape out long strands. Pat dry with paper towels if very moist.

Crisp the bacon: While the squash roasts, cook diced bacon in a large skillet over medium heat until crisp, 6–8 minutes. Transfer bacon to a plate with a slotted spoon. Leave 1–2 tablespoons of fat in the pan; pour off excess.

Sauté garlic: Lower the heat to medium-low. Add minced garlic to the bacon fat and cook 30–60 seconds until fragrant. Don’t brown it.

Make the sauce base: In a bowl, whisk eggs, yolk, and grated cheese until thick and smooth. Season generously with black pepper and a pinch of red pepper flakes if you like. Taste and adjust salt, keeping in mind the bacon and cheese are salty.

Warm the squash: Add the spaghetti squash strands to the skillet with the garlic and toss to coat. If using butter, add it now. Cook 1–2 minutes to heat through. Turn the heat to the lowest setting, or briefly remove the pan from the burner to cool slightly.

Emulsify the carbonara: With the heat low, pour the egg-cheese mixture over the squash while tossing constantly with tongs. The residual heat cooks the eggs gently into a glossy sauce. If it seems too thick, splash in 1–2 tablespoons hot water to loosen.

Finish and serve: Fold in the crispy bacon. Taste and adjust seasoning. Plate immediately with extra cheese and a shower of black pepper. Garnish with parsley if you like.