Level the layers, stack them with filling, then spread a thin crumb coat over the whole cake and chill it for 20 to 30 minutes. That thin first layer traps every loose crumb. Frost properly over the top of it and the finish stays clean.
A homemade cake usually tastes better than a bakery one and usually looks worse, and the gap is almost never skill. It is the crumb coat. Frosting a bare, warm, domed cake drags crumbs into the icing and the layers slide apart while you work. Do the four things below in order and an ordinary cook gets a clean, flat, respectable cake without a turntable or an offset spatula, though both help.
| Cake | Layers | Frosting needed | About |
|---|---|---|---|
| 8-inch round | 2 | 3 cups | 700 g |
| 9-inch round | 2 | 3½ cups | 800 g |
| 8-inch round | 3 | 4½ cups | 1 kg |
| 9 x 13 sheet | 1 | 2½ cups | 570 g |
| Cupcakes | 12 | 2 cups | 450 g |
The cake must be completely cool
Not nearly cool. Completely. Butter frosting melts at barely above room temperature, and a cake that still holds warmth in the middle will turn your icing to soup an hour after you have finished. Two hours on a rack is the minimum for an 8-inch layer; overnight, wrapped, is better and makes the crumb easier to handle.
Level the domes off
Cakes rise higher in the middle, and stacking two domes gives you a cake that rocks and eventually splits. Take a long serrated knife, rest it flat against the top of the pan rim as a guide, and saw the dome off with a gentle back-and-forth. Flip the top layer cut-side down so the flat bottom becomes the top of your cake — that gives you a sharp edge and a smooth surface to work on.
Crumb coat, then chill
Spread a thin, almost transparent layer of frosting over the whole cake. It will look messy and streaked with crumbs, and that is precisely its job: it glues them down. Refrigerate for 20 to 30 minutes until that layer is firm to a fingertip. Everything you spread after this sits on frosting rather than on cake, so no crumb ever reaches the surface.
Frost with more than you think you need
Pile a generous mound on top and push it outward to the edges, then let it fall down the sides and work it around. Spreading a thin amount and adding more is how you drag crumbs up; working from an excess and scraping away the surplus is how bakeries do it. Warm your spatula in hot water and dry it for the final pass to leave a smooth finish.
Questions we get asked
What is a crumb coat and do I need one?
It is a thin first layer of frosting spread over the whole cake to trap loose crumbs, then chilled until firm. You need one on any cake where you want a clean finish. It takes five minutes and half an hour in the refrigerator, and it is the single biggest difference between a homemade-looking cake and a neat one.
How long should a cake cool before frosting?
At least two hours for a standard 8-inch layer, and preferably until it is cold all the way through. Any residual warmth will soften butter frosting and it will slide off the sides an hour later.
How much frosting do I need for a two-layer cake?
About 3 cups for an 8-inch two-layer cake and 3½ cups for a 9-inch. Make more than you think — running short halfway around the sides is far worse than having a little left over.
Why does my frosting pull up crumbs?
You are spreading too thin a layer directly onto bare cake, so the spatula is dragging on the crumb itself. Crumb coat first, chill it, then frost over the top of that. Using more frosting at once and pushing the excess around also helps.
How do you get frosting smooth without special tools?
Dip a palette knife or the back of a large spoon in hot water, dry it, and run it around the cake in one steady pass. The warm metal melts the very surface of the frosting and it settles flat. Repeat, rewarming between passes.
Can you frost a cake the day before?
Yes, and buttercream-frosted cakes are often better for it. Keep it covered at cool room temperature rather than in the refrigerator if you can, because the fridge dries the crumb. Cream cheese frosting must be refrigerated, so let it come back to room temperature for an hour before serving.
Should the top layer go cut-side up or down?
Cut-side down. The flat underside of the cake becomes the top, which gives you a level surface and a crisp edge to frost against.