In a large saucepan, over medium heat, melt butter. Add 4 tablespoons flour and cook for 4 minutes or until flour just starts to brown. Whisk in reserved contents from baking dish and half-and-half. Whisking constantly, bring to a boil, about 5 to 8 minutes, or until thick. Remove from heat and whisk in Gouda cheese. Season with salt and pepper.