Bring a large pot of generously salted water to a boil. Fill a large bowl with ice water.
Cut the tops off the peppers and reserve. Remove the seeds and membranes. Put the peppers and the tops in the boiling water and cook until just tender, 2 to 3 minutes. Plunge the peppers into the ice bath. Once cool, remove them and use a sharp knife to carve a jack-o-lantern face into one side of each pepper.
Return the water to a boil, add the macaroni and cook until al dente, about 6 minutes. Reserve 1 cup of the pasta water and drain (don't rinse the pasta).
Heat the half-and-half in a large saucepan over medium heat until it just comes to a simmer. Continue simmering until reduced to about 3/4 cup, about 10 minutes. Add the cream cheese and stir until melted. Whisk in the Cheddar until all the cheese is melted and the sauce is smooth.
Off the heat, add the macaroni to the saucepan and stir to combine. Stir in some of the reserved pasta water to thin the sauce if needed. Season with salt if needed. Let sit for 10 minutes, then divide the mac and cheese among the peppers and cap each with a pepper top.
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