Red velvet carpet: Microwave sponge cake

Another one from the “I’ve been meaning to try” files, this time prompted in part by a recipe in the latest issue of Lucky Peach. Microwave sponge cakes, pioneered by Albert Adrià, had a brief surge of popularity a few years ago, before retreating back to the relative obscurity of “just another pastry technique.”

There are a few different ingredients that can be used to stabilize foams made in a whipped cream siphon. Gelatin is one of the easiest and most common, but has the drawback that it must be served cold. If you want a warm siphon foam, you have to base it on something else, such as egg whites, which essentially use the siphon to make instant, flavoured meringue. The microwave sponge cake is simply an extension of this, taking that meringue (with a little flour added) and cooking it.

The result is, like aerated chocolate, a “set foam”: when you heat an egg-white foam, the bubbles in it expand, and eventually the egg proteins coagulate, forming a solid matrix and trapping those bubbles forever. That’s more or less how a soufflé works. Only instead of whipping the eggs with a mixer, this cake uses a siphon, and instead of baking it in an oven, you cook it in a microwave.

Although I’d never used this technique before, I decided to try developing my own recipe with it. I made up a spreadsheet of the ingredients in a handful of other recipes I had, and decided the basic ratio of ingredients is about 20 grams of flour, 100g of egg whites, 80g of sugar, anywhere from 0g to 80g of egg yolk, and 120g of your chosen flavour, preferably something that has about 50% fat. I’ve seen recipes using pistachio, chocolate, yogurt and black sesame. There are, of course, outliers to this, but that seemed like a good starting point.

For flavour, I wanted red velvet cake. I’ve had this popular cake only once or twice, but I’m well versed in its distinguishing characteristics: bright red colour, buttermilk, and a hint of chocolate. I devised a recipe that I thought reflected this and would work with this technique. After mixing all the ingredients, straining them, and charging the siphon, I dispensed some into a paper cup with holes punched in the bottom, and microwaved it on high for 40 seconds. Success!

To round out the dessert, I made a beet fluid gel (since beets are sometimes used in the original cake instead of artificial food colouring, and beet pairs nicely with chocolate), cream cheese icing, and candied pecans. I really wanted a green element on the plate, but I couldn’t find any traditional garnish for red velvet cake that was green. And I’m not a fan of the token mint leaf found on so many different desserts.

The one drawback I found to my recipe is that the cakes, left for more than a few minutes, will harden somewhat. I don’t have enough experience with pastry to know what causes this, though it would be nice to be able to refine the recipe so it doesn’t happen. Now that I’m past my “running before you walk” phase, it may be time to take a step back and make one of the professional recipes as a basis of comparison. In the meantime, here’s what I did.


How to make red velvet microwave cake

This recipe should easily serve 6-8 people

100g egg whites
70g egg yolk
80g sugar
20g all-purpose flour
5g cocoa powder
Pinch salt
60g butter, melted
60g buttermilk
Red food colouring, in paste form, as desired

Combine the egg whites, egg yolks and sugar in the bowl of a stand mixer. Whisk for 1 minute on medium speed to combine. Sift the flour and cocoa powder over top, and add the salt. Whisk again until just combined. While whisking, drizzle in the butter and buttermilk, and add the red food colouring until you get the colour you want.

Strain the mixture, and transfer it into a half-litre whipped cream siphon. Charge the siphon with two nitrous oxide cartridges, shaking well after each one. Keep refrigerated.

How to make beet fluid gel

140g beet juice
55g 1:1 simple syrup
1.95g agar

Combine the beet juice and syrup. You can adjust the syrup to taste; just make sure you adjust the agar to be 1% of the total combined weight of the two. Bring to a low simmer, and sprinkle the agar over top, whisking to combine. Bring to a full boil and boil for 1 minute to hydrate the agar. Strain into a heatproof container and allow to set at room temperature.

Once set, cut the gel into cubes, and puree with a blender until the mixture forms a smooth gel. Transfer to a squeeze bottle and reserve in the fridge.

How to make cream cheese icing

150g cream cheese
75g icing sugar
60 ml whipping cream

Beat the cream cheese in an electric mixer until very soft. Sift the icing sugar over top, and beat again until combined, scraping down the sides of the bowl as necessary. Add the whipping cream and beat again until combine. Transfer to a pastry bag fitted with a large plain tip, and reserve in the fridge.

How to make candied pecans
1/4 cup granulated sugar
1 Tbsp. white corn syrup
1 Tbsp. water
25 pecan halves

Preheat the oven to 350°F. Spread the pecan halves on a baking sheet, and place in the oven. While they cook, combine the sugar, corn syrup and water in a saucepan. Heat over medium heat until the sugar caramelizes. Immediately remove the warmed pecans from the oven, add to the caramel, and stir to cook. Spread on a parchment-lined baking sheet, keeping each pecan half separate, and allow to cool. Break off any extra caramel, transfer to an airtight container, and reserve.

To plate the dessert

Pipe random dots of cream cheese icing and beet gel onto a plate. Take a 9-oz paper cup, poke four holes in the bottom, then dispense the microwave red velvet cake batter into the cup, filling halfway. Microwave on high for about 40 seconds (you may have to adjust the time, depending on the power of your microwave). Allow to cool briefly, then run a thin-bladed knife around the inside of the cup to loosen the cake. Tear in half and place on the plate. (I cooked 6 microwave cakes for 4 servings, allowing one and a half per person.) Lean candied pecans against the cream cheese icing.

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