16 oz. Conchigliette Pasta, (small shells)
2 tablespoons + 2 teaspoons White Miso
1 tsp. Morton Kosher Salt, plus more
4 cups Whole Milk
1¼ tsp. Garlic Powder
1 tsp. freshly Ground Black Pepper
½-⅔ tsp. Crushed Red Pepper Flakes, plus more for serving
6 tbsp. Unsalted Butter
⅔ cup All-Purpose Flour
12 oz. Sharp Yellow Cheddar, coarsely grated
Cook pasta shells in a large pot of boiling salted water, stirring occasionally, until al dente. Drain, reserving 1 cup pasta cooking liquid (do not rinse pasta). Add pasta to a large mixing bowl and set aside.
Whisk whole milk, white miso, garlic powder, freshly ground black pepper, kosher salt, and crushed red pepper flakes in a small saucepan to combine, then bring to a simmer over medium-high heat.
Meanwhile, melt unsalted butter in a large pot over medium-low heat. Sprinkle all-purpose flour over and cook, whisking constantly, until combined and mixture is foaming but still very pale, about 4-6 minutes.
Whisking constantly to prevent lumps from forming, very gradually pour in 1¼ cups hot milk mixture, then cook, still whisking constantly, until smooth. Add remaining milk mixture and whisk again until smooth. Add sharp yellow cheddar, coarsely grated, and ½ cup pasta cooking liquid and cook, whisking, until cheese is melted and sauce is smooth once more. Add to reserved pasta and stir, adding more pasta cooking liquid to loosen sauce if needed. Serve when pasta is well coated.