Roast the garlic: Preheat oven to 200°C (400°F). Slice the top off the whole garlic bulbs (the 120 g portion) to expose the cloves, drizzle lightly with olive oil (about 1 tsp per head), wrap tightly in foil and roast for 30–35 minutes until cloves are soft, deeply golden and caramelized. Why: Roasting transforms raw garlic’s harsh bite into a sweet, buttery purée that gives the sauce rounded, savory-sweet backbone without raw pungency.

Make roasted garlic purée while hot: When the bulbs are cool enough to handle, squeeze the soft cloves into a small bowl, mash with a fork and blend with 1 tbsp olive oil into a smooth purée (or blitz in a small food processor). Taste and add a pinch of salt. Why: Blending the roasted cloves with oil gives a spreadable, emulsified base that will coat the pasta evenly and melt into the sauce for silky texture.

Prepare garlic chips: Thinly slice the 36 g fresh garlic cloves very thin (use a mandoline or sharp knife). In a small skillet, heat 2 tbsp (30 ml) olive oil over medium-low heat until shimmering but not smoking. Add the garlic slices in a single layer and fry until just golden around the edges (about 1–2 minutes), stirring constantly. Transfer to a paper towel to drain and immediately season with a pinch of salt. Why: Frying on medium-low prevents burning — golden chips add contrasting texture and a sharper garlic note that pops against the mellow roasted purée.

Bring a large pot of water to a vigorous boil and add 12 g kosher salt. Add the 400 g spaghetti and cook until al dente according to package directions (typically 8–10 minutes). Reserve 1¼ cups (300 ml) of the pasta cooking water before draining. Why: Salted pasta water seasons the noodle internally, and the starchy reserved water is the key to creating an emulsion between oil and purée for a glossy, clingy sauce.

Build the sauce in a wide sauté pan: Over medium heat, melt the 40 g butter with the remaining 5 tbsp (about 50 ml) olive oil. Add the roasted garlic purée and red pepper flakes; cook, stirring, for 1–2 minutes to warm the purée and 'bloom' the red pepper flakes. Why: Gently warming the purée allows its flavors to open and integrates the fat so the garlic flavors infuse the oil without developing bitterness.

Finish the pasta in the pan: Add the drained spaghetti to the sauté pan along with ¾ cup (180 ml) reserved pasta water. Toss vigorously with tongs for 1–2 minutes until the sauce emulsifies and the pasta is well coated; add more reserved water as needed for a glossy, loose sauce. Stir in the lemon juice and chopped parsley, then taste and adjust seasoning with salt and black pepper. Why: Tossing with starchy water creates a silky emulsion (like a very light beurre monté) so the oil and purée cling to the pasta instead of separating.

Finish with cheese and garlic chips: Remove pan from heat, add grated Parmesan if using and toss to combine; finish with the crispy garlic chips scattered on top and a final drizzle of good olive oil. Why: The cheese adds savory umami and creaminess; the chips give temperature and textural contrast, turning a simple aglio e olio into a restaurant-quality plate.

Plate and serve: Divide pasta among warm bowls, garnish with extra parsley, a light grind of black pepper and an optional lemon wedge. Serve immediately. Why: Serving hot preserves the glossy sauce and keeps the garlic chips crisp for the best mouthfeel.