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1
Toss bread crumbs with butter in small bowl until combined. Set aside.
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2
In food processor or blender, process cheddar, Parmesan, and ricotta until no large pieces of cheese remain, 1 to 2 minutes. Transfer to bowl and set aside.
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3
Adjust oven rack to lower-middle position and heat broiler. Bring 4 quarts water and 1 tbsp table salt (not in ingredient list) to boil in Dutch oven over high heat. Add macaroni and cook until tender, 7 to 9 minutes. Drain macaroni and leave in colander.
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4
In now-empty Dutch oven, heat butter over medium-high heat until foaming. Add flour and mustard and cook, whisking to combine ingredients, until mixture is smooth, about 1 minute. Whisking constantly, slowly add milk and Tabasco, if using, and bring to full boil. Reduce heat to medium and simmer, whisking frequently, until mixture becomes slightly thicker than heavy cream, 2 to 4 minutes. Remove pan from heat. Whisk in cheese mixture and 1/2 teaspoon salt until cheese is melted. Add pasta and cook, stirring constantly, over medium-low heat, until mixture is steaming, 2 to 3 minutes.
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5
Transfer mixture to broiler-safe 8-inch-square baking dish and sprinkle with bread crumbs. Broil until crumbs are deep golden brown, 2 to 4 minutes, rotating pan if necessary for even browning. Cool 2 minutes. Serve.
