Crumb-coating is essentially a thin layer of icing used to glue down crumbs and provide an even base so that your decorative icing can be a flawless masterpiece. If you think of your cake as a wall you’re about to paint, then the crumb coat is the basecoat.
You don’t even have to save it for a special occasion cake, most cakes can benefit from a crumb coat.
Now before you crumb coat your cake, if your cake has multiple layers then make sure you cut your cake, and ice in between your cake layers and stack them first. Chill the cake for 30 minutes to prevent the multiple layers from sliding around and potentially making a big mess.
Once your assembled, and hopefully structurally sound cake is chilled, then you’re ready for the crumb coat. Simply use an offset spatula, nylon spreader, or table knife to spread a very thin layer of frosting over your cake. It should cover the sides and top of your cake.
It only needs to be a thin layer; you want to still be able to see the cake underneath (think a naked cake). Smooth the icing and let it dry until it feels dry to the touch. It needs to be dry before applying your final layer of icing, if you’re in a rush you can chill the cake to dry it faster.
That’s it, that’s the crumb coat done. Now you’ll just have to actually ice the cake!