In the meantime, make a paste out of the remaining melted butter and the flour. Stir it into the mixture in the saucepan and cook until thickened and the liquid comes to a boil. Remove the pan from the heat, transfer the mixture to the prepared dish (or ramekins), and sprinkle with the remaining 1/3 cup cheese. Diva Do-Ahead: At this point, you can let cool, cover, and refrigerate for up to 3 days or freeze for up to 1 month. Bring to room temperature before continuing.