Set an oven rack in the upper third of the oven and preheat the oven to 375 degrees F.
Bring a large pot of salted water to a boil. Add the macaroni and cook until al dente, about 5 minutes. Strain, reserving 1 3/4 cups of the pasta water. Set strained pasta and reserved water aside.
Melt the canna-butter and butter in a large pot over medium heat. Add the chopped jalapenos to the saucepan and cook, stirring, until softened, about 5 minutes; transfer to a small bowl and reserve.
Add the half-and-half to the saucepan. Cook over medium heat until it just comes to a simmer. Continue simmering until the half-and-half is reduced to 1 1/2 cups, about 10 minutes.
Add the cream cheese and stir until melted.
Whisk in the Cheddar and Pepper Jack until all the cheese is melted and the sauce is smooth.
Stir in the macaroni and reserved pasta water until mixture is well combined.
Season with cayenne, salt and pepper.
Pour into a 13-by-9-inch baking dish. Don’t worry if things look soupy, the macaroni will absorb lots of sauce as it bakes.
Mix the panko crumbs with 1/4 cup melted butter.
Spread an even thin layer of buttered bread crumbs over the top of the pan.
Arrange jalapeno slices on top of the breadcrumbs.
Bake until filling is bubbly and topping of lightly browned, about 20 minutes.