Melt butter in large saucepan on low heat. Add flour and seasonings; cook and stir 2 min. or until hot and bubbly. Gradually whisk in milk; bring just to boil on medium heat, stirring constantly. Simmer on medium-low heat 3 to 5 min. or until thickened, stirring constantly. Gradually add cheddar, cooking and stirring after each addition until melted. Remove from heat. Add squash purée; mix well.