In a medium saucepan over medium-high heat, melt the butter. Add the celery and onion and cook for 2 to 3 minutes, stirring occasionally. Add the remaining ingredients and whisk together. Bring to a boil, reduce heat, cover, and simmer for 15 minutes, stirring occasionally. Transfer to a bowl, cover with plastic wrap, and refrigerate until ready to use. Makes about 1 1/3 cups.