4. Step
Remove the steamer basket from the pot; dry the pot. Add butter and melt over medium-high heat. Add garlic, sage and mustard; cook, stirring, until fragrant, about 1 minute. Add the squash puree and cook, stirring occasionally, until simmering, about 2 minutes. Remove from heat and add Cheddar, Parmesan, salt and pepper, stirring until smooth. Stir in the pasta. Serve garnished with more sage, if desired.