Icing is the part people skip reading about and then rush at the last minute. Most of what goes wrong - grainy texture, air bubbles under the spatula, frosting sliding off the cake - comes from two or three decisions made before the mixer is switched on.
The ten steps below follow John Kanell of Preppy Kitchen, and they make American buttercream: butter, powdered sugar, a splash of cream, vanilla, salt. Ten minutes, no thermometer. What follows here is what the steps do not have room for. Which buttercream to make. How to rescue a batch that breaks. How to get the consistency right for the thing you are frosting.
American, Swiss, or Italian: Pick One Before You Start
American buttercream is butter beaten with powdered sugar. Sweetest of the three, forms a light crust as it sits, pipes sharp edges. That crust is why it is the standard for cupcake swirls and borders.
Swiss meringue buttercream starts with egg whites and sugar warmed over a pot of water, whipped to a meringue, then loaded with butter. Silkier, much less sweet, three times the work. Italian goes further still: hot sugar syrup poured into whipping whites. It is the most stable of the three in a warm room.
Royal icing is a different animal. No butter, no cream, it dries hard, and it is what you want for flooding and detail work on cookies. If that is the job, use royal icing instead.
Why Buttercream Splits, and How to Bring It Back
Almost every broken batch is a temperature problem. Butter that came out of the fridge an hour ago looks soft outside and is still cold in the middle, so the cream will not emulsify into it and you get curds instead of frosting. Wrap a warm, damp towel around the bowl for a minute and keep the mixer running on low. It pulls back together.
The opposite happens in a hot kitchen. Soupy, sliding buttercream means the butter went past soft into greasy. Put the bowl in the fridge for 15 minutes, then rewhip on low.
Grit is a different problem. That is sugar that never dissolved, and another three or four minutes on low usually fixes it.
Consistency for Spreading, Piping, and Flooding
The same bowl of buttercream does three jobs, and the only variable is liquid.
- Spreading on a cake: soft enough to drop off the spatula in a blob. Add a fourth tablespoon of cream.
- Piping swirls and borders: holds a peak that curls slightly at the tip. That is the recipe as written.
- Piped flowers and stiff rosettes: hold back the last tablespoon of cream and beat in another half cup of powdered sugar.
- A thin glaze for drizzling: not this recipe at all. Powdered sugar and about a tablespoon of milk per cup, whisked in a bowl by hand.
Coloring It Without Thinning It Out
Use gel color, not the liquid bottles in the baking aisle. Liquid coloring is mostly water, and enough to turn a batch deep red will slacken the buttercream until it will not hold a shape. Deep shades need time more than they need more dye: mix the gel in, cover the bowl, and leave it a few hours. Red and black both darken as they rest. For chocolate buttercream, cool the melted to barely warm before beating it in. Hot chocolate melts the butter on contact.
Make It Ahead and Keep It
Buttercream keeps 3 to 4 weeks in the fridge and 2 to 3 months in the freezer, sealed in an airtight container or a tied piping bag. Worth doubling the batch: frost a cake this week and the rest waits for the next one.
Bring it to full room temperature on the counter first, which takes 2 to 3 hours for a large container. Do not microwave it. Beat it on low for a minute to knock out the air. It will look separated when it starts moving. Keep going.
The obvious places to put a batch are sugar cookies and a tray of gingerbread cookies. If half a bag of powdered sugar is still there afterward, fudge uses it up.
