Optional: If baking mac and cheese, preheat oven to 325° Fahrenheit. Lightly grease 9x13 baking dish with butter or neutral-flavored cooking spray. Set aside.
Add 3 cups shredded fresh white cheddar and 3 cups shredded fresh smoked gouda to medium bowl. Mix cheeses together by hand until well blended. Set aside.
Place medium saucepan on stovetop over medium heat. Add ½ cup unsalted butter to saucepan and let butter melt completely.
Once butter has melted, sprinkle ½ cup all-purpose flour over melted butter. Whisk butter and flour together vigorously to combine, then cook roux 1 minute, whisking frequently.
After 1 minute, remove saucepan from heat. Add 2 cups half-and-half in small increments, whisking constantly. Continue until all half-and-half has been added to saucepan and mixture is mostly smooth.
Add 2 cups whole milk to mixture and whisk well until milk is fully incorporated and mixture is completely smooth, with no lumps remaining.
Return saucepan to medium heat and simmer, whisking often, until mixture becomes very thick, approximately 5 minutes.
Once mixture has thickened, remove saucepan from heat and let cool slightly. Add 1 ½ teaspoons salt, ½ teaspoon fresh cracked black pepper, and 1 teaspoon truffle oil and whisk to incorporate.
Once seasonings are incorporated, add 3 cups of shredded cheese blend, stirring constantly until cheese has melted and is fully incorporated.