Melt butter in a saucepan. Add white and brown sugars and bring to a boil, stirring constantly. Stir in cream and return to a boil. Boil, stirring constantly, for exactly 2 minutes. Remove from the heat and stir in salt.
Allow glaze to cool completely, 30 to 45 minutes. Place in the refrigerator to chill, 8 hours to overnight.
You can use either light brown or dark brown sugar in this glaze.