Sacher torte with the Thermomix, moist with a glossy chocolate glaze

A true Sacher has a compact, moist sponge, not overly light: that's why the batter uses equal parts chocolate, butter, sugar and flour, the classic Austrian formula. The layer of jam under the glaze isn't decorative: it helps the chocolate stick perfectly and keeps crumbs from mixing into the coating.

The whipped egg whites: the step that decides everything

There's no leavening magic in this recipe: the structure comes almost entirely from the air you beat into the egg whites. That's why they're whipped first, in a perfectly clean, dry bowl.

Even a trace of fat or a speck of yolk stops egg whites from whipping properly: it's chemistry, not bad luck. If a bit of yolk falls into the white while separating the eggs, lift it out with a piece of eggshell (it works better than any spoon) or set that white aside.

The pinch of salt helps stabilize the foam. And when you fold them into the batter, go from the bottom up and take your time: every rough movement is lost air, meaning a flatter cake.

Why apricot jam, and not something else

It's not a random tradition: apricot has just the right acidity to balance the double dose of chocolate between the sponge and the glaze. With a sweeter jam, like strawberry or peach, the cake ends up cloying.

If yours has whole fruit pieces, blend it first: a smooth layer spreads evenly and lets the glaze sit perfectly. If it's very thick, warm it for a few seconds to loosen it.

The outer layer of jam isn't decorative

It's the bakery trick that makes the difference between a smooth, mirror-like glaze and one full of crumbs. Spreading a thin layer over the whole outer surface seals in the sponge's crumbs and creates an even surface for the chocolate to flow over without snagging.

Skip this step and the glaze drags bits of cake with it, leaving the result dull and uneven.

How to get a mirror-like glaze

Three rules:

• Pour it warm, not boiling hot: too hot and it turns runny, leaving too thin a layer.
• One single pour, from the center: pour it in the middle and let gravity spread it toward the edges. The more you touch it with a spatula, the less glossy it stays.
• Cake on a rack, with a plate underneath: the excess glaze drips away instead of pooling around the base.

Let it set at room temperature, never in the fridge: the cold dulls the chocolate and can create condensation on the surface.

How to serve it (and store it)

In Austrian tradition, Sacher torte is served with a dollop of unsweetened whipped cream: the contrast with the sweet glaze is intentional, cutting through the richness of the chocolate.

It keeps at room temperature, under a cake dome, for 3-4 days. If anything, it's even better from the second day on: the jam has time to moisten the sponge. Only refrigerate it if your kitchen runs very warm, but take it out at least an hour before serving.