While I love and recommend a cream cheese frosting with this cake, you can make a flour-based frosting by using 1 cup milk, ¼ cup all-purpose flour, ⅛ teaspoon kosher salt, 1 cup butter (room temperature), 1 ½ cups powdered sugar, and ½ teaspoon vanilla. In a medium saucepan whisk milk, flour, and salt together on medium-low heat until it thickens (like a gravy). Remove the pan from heat and allow it to cool (stirring occasionally). In the bowl of a stand mixer beat butter until light and fluffy. Add in cooled flour mixture and vanilla, and mix until combined (2-3 minutes). Frosting will be thick and smooth.