Preheat to 375°F (190°C). Lightly grease a standard 12-cup muffin tin with cooking spray or brush with oil. Don't skip this—stickage is real.
Boil macaroni in salted water until just shy of al dente (about 1 minute less than the package). Drain well. Slightly undercooked pasta holds up better in the oven.
In a saucepan over medium heat, melt 2 tbsp butter. Whisk in flour and cook 1 minute to make a roux. Slowly whisk in milk until smooth. Simmer 2–3 minutes until lightly thickened.
Reduce heat to low. Stir in cheddar, mozzarella, and Parmesan until melted and smooth. Add Dijon, garlic powder, onion powder, smoked paprika, salt, and pepper. Taste and adjust seasoning.
Remove from heat. Stir in sour cream or Greek yogurt. Let cool for 2 minutes, then whisk in the beaten egg quickly so it doesn't scramble. This egg is your structural integrity.
Fold the sauce into the drained pasta. If using mix-ins (bacon, veggies, jalapeños), fold them in now.
Mix panko with melted butter or olive oil and a pinch of salt and pepper. For extra drama, add a spoonful of Parmesan.
Divide the mac mixture among the 12 cups, packing it down gently with a spoon to help it set. Top each with a spoonful of the panko mixture. Press lightly.
15–18 minutes, until the tops are golden and edges are sizzling. You're going for crisp edges, not burnt offerings.
Let them cool in the pan 8–10 minutes. Run a butter knife around the edges and pop them out. If they resist, wait another 3 minutes. Patience beats broken bites.
Hot with a sprinkle of chives, a drizzle of hot honey, or a dash of hot sauce. Try not to inhale them all at once. Or do—no judgment.