Bring a large pot of water to a rolling boil. Add 1 tablespoon kosher salt. Add 12 oz fresh egg pasta and cook until al dente, 2–4 minutes (follow package guidance). Reserve 1 cup pasta cooking water, then drain pasta and set aside briefly.

Swiss cheese fondue

Make a roux

In a medium saucepan over medium heat, melt 2 tablespoons unsalted butter. Add 2 tablespoons all-purpose flour and whisk continuously for 1–2 minutes until it bubbles and the raw flour smell dissipates but it does not brown.

Add liquids

Slowly whisk in 1.5 cups whole milk and 1/2 cup dry white wine (or use all milk if omitting wine). Continue whisking and bring mixture to a gentle simmer. Cook 2–3 minutes until slightly thickened.

Season and finish

Whisk in 1 teaspoon Dijon mustard, 1/8 teaspoon grated nutmeg, 1/2 teaspoon salt, and 1/4 teaspoon freshly ground black pepper. Lower heat to low. Gradually add 8 oz grated Swiss cheese in small handfuls, stirring or whisking after each addition until fully melted and smooth. If the sauce is too thick, whisk in up to 1/2 cup reserved pasta water a few tablespoons at a time to reach a smooth, pourable fondue consistency.

Combine and finish

Return drained pasta to the pot or a warm skillet set over low heat. Pour the Swiss cheese fondue over the pasta and toss gently to coat. Add reserved pasta water a few tablespoons at a time if needed to loosen the sauce so it evenly coats the pasta.

Fold in 1 cup diced tomato and 1/2 cup thinly sliced green onions, reserving a small sprinkle of green onion for garnish.

Stir in 1 cup shredded cheddar jack cheese until just combined and slightly melted into the pasta.

If desired, stir in 1 tablespoon unsalted butter for extra gloss and richness.

Transfer to a serving dish or keep in the warm pot. Top with 6 slices cooked crisp Bristol bacon that have been chopped into bite-sized pieces. Garnish with the reserved green onion slices and an extra grind of black pepper.