Bring a large pot of salted water to a rapid boil (use about 1.5 liters / 6 cups for 160 g pasta). Salt the water generously — it should taste like the sea — because this is your only chance to season the pasta’s interior. Cook the gluten-free penne 1–2 minutes shorter than package directions for truly al dente texture; it will finish cooking in the sauce and won’t go mushy.

While the water heats, pat the shrimp dry with paper towels and season lightly with salt and freshly cracked black pepper. Drying the shrimp removes surface moisture so they sear instead of steam, giving better texture and flavor.

Heat a large (12"/30 cm) skillet over medium-high heat. Add the olive oil and swirl to coat. When the oil is shimmering but not smoking (this temperature allows quick color without burning), add half the minced garlic and a pinch of red pepper flakes if using. Sauté 20–30 seconds until fragrant — this quick bloom softens raw garlic’s bite and infuses the oil with aroma.

Add the halved cherry tomatoes cut-side down in a single layer. Cook undisturbed for 3–4 minutes so the cut sides blister and caramelize; this unlocks natural sugars and creates a sweet-tart base for the sauce. Toss and continue cooking 1–2 minutes until tomatoes begin to collapse and release juices.

Push the tomatoes to one side of the pan, increase the heat briefly to medium-high, add the shrimp in a single layer and cook 1.5–2 minutes per side (depending on size) until pink and just opaque. Sear quickly to keep shrimp tender — overcooking makes them rubbery. Stir shrimp with the tomatoes for the last 30 seconds to marry flavors.

Reserve 1 cup (240 ml) of the pasta cooking water, then drain the penne. Add the hot, drained pasta directly to the skillet with tomatoes and shrimp. Pour 3–4 tablespoons (45–60 ml) of the reserved pasta water into the pan. Toss vigorously over medium heat — the starches in the water will emulsify with the oil and tomato juices to create a glossy, clingy sauce that coats each pasta tube.

Turn the heat to low, add the baby spinach and most of the torn basil, and sprinkle the grated Parmesan over the pasta. Toss until the spinach wilts and the cheese melts into the sauce, about 1 minute. The residual heat is enough to wilt greens without overcooking them, preserving color and texture.

Taste and adjust seasoning with salt and pepper. If the sauce feels tight, add another tablespoon of reserved pasta water. Serve immediately, finishing each bowl with the remaining basil and an extra sprinkle of Parmesan and a twist of black pepper.

Optional finishing touch: For a little extra gloss and richness, add a teaspoon of cold extra-virgin olive oil to each serving just before plating; it brightens flavors and gives a restaurant-style sheen.