Preheat the oven to 375° F. Spray a 9x13-inch casserole dish with nonstick cooking spray and set aside.
Prepare the pasta according to package directions until pasta is al dente. Before draining the pasta after cooking, set aside one cup of the pasta water. Then drain pasta and set it aside (you’ll need the pot for later).
Prepare the panko topping. Melt 2 Tablespoons of unsalted butter in a small bowl in the microwave. Then stir in the panko breadcrumbs, parmesan cheese and a pinch of kosher salt and pepper. Set the topping aside.
In the same pot you used to cook the pasta, melt the remaining 2 Tablespoons of unsalted butter over medium heat. Add in the chopped onions and cook until they become soft and translucent (it should take about 2 minutes).
Sprinkle 3 Tablespoons of all-purpose flour over the onions and stir until a thick paste forms.
Add the dijon mustard and reserved pasta water to the pot, continuing to stir until the mixture becomes smooth (this could take a few minutes). You may find this easiest if using a whisk.
Add in the Boursin cheese and season with a pinch of salt and pepper. Stir to break up the cheese and to help it melt.
Once it has started to melt, add in the diced ham, gouda cheese and heavy cream to the pot. Cook the mixture over low to medium heat until all the ingredients are melted and combined well.
Remove the pot from the heat and add in the cooked pasta. Stir until pasta is evenly coated with the sauce mixture.
Transfer the pasta mixture into the prepared casserole dish. Sprinkle the panko topping (that you set aside earlier) evenly on top.
Place the casserole dish on the middle oven rack in the oven and bake uncovered for about 15-20 minutes (or until the topping turns golden brown).
Top the casserole with a bit of chopped parsley (optional). Allow the casserole to cool for 5 minutes before serving.
Notes
Please refer to my FAQ’s and ingredient list above for other substitutions or for the answers to the most common questions.
Don't let the different cheese options steer you away from this recipe, I have other ideas you can use instead in the ingredient listing.
This is a great recipe to use up leftover ham.
Store leftovers in the fridge for up to 4 days in an airtight container.