Prep the sweet potato:
Peel sweet potato and chop into 1 inch pieces. Place sweet potato cubes in a microwave safe bowl or steamer. Cover potatoes with water. Place cover over bowl/steamer and microwave on high for 5 minutes or until cubes are easily pierced with a fork.
Drain water from potatoes, reserving 1/4 cup of the liquid. Let stand 10 mins to cool.
Place cooked sweet potatoes into a food processor or blender. Add 2 Tbsp of reserved water and puree until no lumps remain, adding additional water, 1 Tbsp at a time, as necessary.
For the cheese sauce:
Melt butter in a large skillet. Whisk in flour and cook - stirring continuously - until the butter/flour mixture begins to brown.
Whisk in milk, dijon mustard, cheddar cheese, salt, nutmeg, and pepper.
Stir in sweet potato puree.
Mash 4-5 cloves of roasted (not raw) garlic.
Add garlic to sauce, stirring to incorporate.
Taste your sauce and add more salt or pepper depending on your preference.