Melt the butter. Set your frying pan or medium saucepan over a medium heat. Add the butter and watch it foam, then subside — you'll see tiny bubbles that smell nutty and rich. This takes about 1 minute.

Cook the onion. Tip in the diced onion. Stir it with a wooden spoon; you want it to turn translucent and soft, not brown. After 3 to 4 minutes, the pieces will look glossy and you'll smell a sweet, mellow aroma.

Add the garlic and flour. Stir in the minced garlic and the flour. Cook for a full minute, stirring constantly. The mixture will become a thick, pale paste (a roux) that clings to the spoon and smells toasty.

Pour in the milk. Slowly add the milk while whisking vigorously. You'll hear a satisfying sizzle as it hits the hot pan. Keep whisking until the mixture thickens enough to coat the back of your spoon — about 2 minutes. The colour will be a pale cream.

Melt the cream cheese. Drop in the cubes of cream cheese. Stir gently. Within 1 to 2 minutes, the sauce will become glossy and smooth, with no white flecks remaining. The texture should look like thick double cream.

Add the grated cheeses. Reduce the heat to low. Add the cheddar and Monterey Jack a handful at a time, stirring after each addition. You'll see the cheese strands disappear into the sauce, turning it a deep, golden yellow. The smell is incredible — rich, sharp, and comforting.

Stir in the remaining ingredients. Fold in the diced tomato, drained green chillies, cumin, and smoked paprika. The sauce will look speckled with red and green. Taste it — you should get a gentle warmth from the spices and a fresh pop from the tomato.

Season and serve. Add salt and pepper to your taste. If the dip seems too thick, stir in a splash of warm milk. Garnish with fresh coriander if you like. Serve immediately while it's hot, smooth, and oozing.