Preheat oven to 400 degrees and spray an 8x8" baking dish with vegetable oil spray.
In a large pot boil the pasta for 5 minutes then drain and set aside.
In that pot, wipe it dry with a paper towel.
On medium-high heat melt the butter and whisk in the flour until the flour is completely mixed in.
Add in the milk slowly whisking as you pour.
Cook, stirring constantly, for 5-6 minutes until the sauce starts to thicken.
Add in 1 1/2 cups of the cheddar cheese and the cottage cheese whisking well.
Add salt, mustard, pepper, and the cooked pasta and stir to combine.
Pour mixture into baking dish.
Bake, uncovered for 25-30 minutes or until golden brown and bubbly.