Moms Creamed Spinach à la Julia

Name: Mom's Creamed Spinach à la Julia
Ingredients: 10 ounces washed spinach; 2 tablespoons to 3 tablespoons unsalted butter (or more); 2 tablespoons to 3 tablespoons all-purpose flour; 1/4 teaspoon freshly grated nutmeg; 1/2 Knorr stock cube; 1 cup water; Kosher salt, to taste; Freshly ground black pepper, to taste