Preheat oven to 450 degrees F. Place poblano peppers on a sheet pan and roast for 45 minutes, until charred and brown. Remove from oven and put the peppers into a brown bag to steam. After 10 minutes, remove and peel skin off the peppers, and discard seeds and skin. Dice peppers. (You can do this two days ahead of time.)
In a saucepan, melt butter over medium heat, then add sweet rice flour. Stir constantly for one minute, to cook the flour. Add milk and cream, stirring. Bring to a light simmer, and cook for 8-10 minutes, until liquid is thickened to the consistency of heavy cream. Add cumin,1/2 teaspoon salt, garlic powder, red pepper flakes.
Remove from heat and add 1/2 of Chihuahua cheese, stirring in figure 8's to melt. Then add remaining amount and repeat.
While sauce is cooking, bring a large of water to a boil with 1/2 teaspoon salt, and cook macaroni according to directions. Drain when al dente.
Put drained noodles back into their large pot, and add cheese sauce, diced green chiles, and diced poblanos. Stir until completely coated. Top with crumbled queso and extra red pepper flakes. Serve.
Leftovers will stay good for 3 days in refrigerator.