Cutting carbs? Limiting Gluten? Sub in a chickpea pasta (such as banza). It cooks up and tastes a lot like regular pasta but packs extra protein and lacks gluten and wheat.
Grease a 9x13-inch baking dish. Cook macaroni until al dente; drain. Preheat oven to 350*F.
Meanwhile, melt 2 Tbsp. butter in a small saucepan over medium-high heat. Whisk in flour to form a paste. Add milk and bring to a boil, whisking constantly. Boil, whisking, 1 minute more. Stir in salt and black pepper. Remove from heat.
Add half of macaroni to prepared dish, followed by half of onion and half of each cheese. Repeat layers. Pour sauce over top. Dot top with remaining 2 Tbsp. butter.
Cover with foil; bake until cheeses are melted, about 30 minutes. Top with cracked black pepper.
Put the pasta in a pot with enough cold water to bring the level about 1 1/2 over the dry noodles. Turn the heat to medium/high heat. Salt the water. Bring the water to a rolling boil until the pot is "just about to boil over". Then TURN IT OFF & STIR ONCE to make sure the noodles are not sticking together. Then PUT THE LID BACK ON and just wait until the noodles swell and look done. (maybe 10 minutes with the lid on)
*if using an electric range, you may have to move the pot off the hot burner when it's time to turn the heat off*
Serving Size 3/4 cup
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.