Plus: More Seafood Recipes and Tips
Bring 1 quart of water to a boil in a medium pot. Add the spinach and cook until very tender and the water is green, 5 to 6 minutes. Drain the spinach in a colander set over a large bowl and reserve 2 3/4 cups of the cooking liquid. Let the spinach sit until cool enough to handle, then finely chop, and set aside.
Melt the butter in a medium pot over moderately high heat. When the butter is foamy, add the onions, celery and garlic and cook, stirring, until softened, about 3 minutes. Add the reserved spinach water, bring to a boil and cook for 1 minute. Add the chopped spinach, liqueur, salt and pepper and simmer, stirring occasionally, until the mixture reduces slightly, about 10 minutes. Remove from the heat, add the cracker meal and food coloring, and stir well to combine. Cool completely before using.
The sauce can be refrigerated for up to 3 days.