Prep Time 15 minutes mins
Cook Time 15 minutes mins
Total Time 30 minutes mins
Don't skip the mustard: It doesn't taste like mustard in the final dish – it adds that diner burger tang.
Freshly grated cheese is essential: Pre-shredded cheese contains anti-caking agents that make the sauce grainy. Grate your own sharp cheddar.
Storage: Store leftovers in the fridge for up to 3 days. Add a splash of milk when reheating. Freezes well – thaw overnight and reheat gently.
Variations: For a spicy version, add a diced jalapeño with the onion and a pinch of cayenne with the flour. Add frozen peas or spinach at the end for extra veggies. For gluten-free, use a 1:1 gluten-free pasta blend and gluten-free flour.