Rocher Roulade

Eggs here are doing two jobs, not one: structure and lift. Four eggs for 100g of flour is a lot of egg relative to flour — that ratio is what makes the sponge thin and elastic rather than cakey. Don't swap in fewer, larger eggs and call it close enough; the whisking time to get "light and fluffy" depends on egg volume, and a short-changed whisk means a short-changed rise.

Nutella appears twice, and it's doing different work each time. In the batter, 40g is there for softness and that faint hazelnut-chocolate note running through the sponge itself, so the roulade doesn't taste like plain cake with filling — it tastes like one thing. In the filling, 100g folded into whipped cream is there for flavour you actually bite into, not just smell. If you're out of Nutella, any hazelnut-chocolate spread with a similar fat content will behave the same way; plain chocolate spread without nuts works too, you just lose the crunch-adjacent flavour, not the mechanics.

Baking powder at 8g for 100g flour is a brisk amount — it's compensating for the weight of the Nutella and eggs, giving the sponge the extra lift it needs to stay thin and open rather than dense. Sift it with the flour, not after, so it's distributed evenly; a pocket of unmixed baking powder shows up as a bitter spot and an uneven crumb, which you'd then wrongly blame on the oven.

The milk (or sugar water) brushed over the sponge before filling is a small step that prevents a real problem: a bare sponge surface dries and toughens slightly as it sits, and a tough surface is exactly where a roll wants to crack. A thin coat of liquid keeps that surface pliable right up until you've rolled it. Tea-with-milk households will have milk open anyway — use what's in the fridge, it doesn't need to be anything special, it just needs to be wet.

Double cream for both the filling and the glaze is doing structural work, not just richness — it's the fat content that lets it whip to stiff peaks for the filling and lets it melt smoothly into the chocolate for the glaze without splitting. Lower-fat cream will whip softer and won't hold the roll's shape as firmly, and in the glaze it can separate instead of binding with the melted chocolate. If you're substituting, look for cream at or near 48% fat — that's the criterion, not the brand.

Milk chocolate in the glaze matters for melting behaviour as much as sweetness: it has enough cocoa butter to melt smoothly with warmed cream into a pourable glaze rather than seizing. Dark chocolate will set harder and taste sharper against the sweet filling; if that's what you have, add a touch more cream to keep it pourable rather than stiff. The hazelnuts folded in last aren't decoration — they're there to be felt, the one place in the whole dessert where something actually crunches against all that soft cream and sponge, which is the point of calling it "Rocher" at all.

On an ordinary UK hob and oven: the 180°C fan/non-fan split in the steps already accounts for the fact that your oven runs one way or the other, so follow whichever applies and trust the look of it over the clock — pale gold, just set, slightly springy when pressed, not browned at the edges. And patience is the real missing ingredient twice over here: the 120 minutes in the fridge isn't a suggestion you can shorten because you're hungry, it's the time the cream needs to firm against the sponge's own weight, and rushing it gets you a roulade that oozes the second you slice it rather than holding a clean spiral.