Egg White Ciambella Cake

Flour and potato starch together, not flour alone — the starch is there to dilute the gluten. Less gluten means a more tender, finer crumb instead of something chewy and bready. If you don't have potato starch, cornflour does the same diluting job; just don't swap in more flour to make up the weight, that defeats the purpose.

The oil instead of butter isn't a health substitution dressed up as tradition — it's simpler mechanics. Butter has to be softened or melted and behaves differently depending on its temperature; oil is liquid at room temperature always, so it blends into the sugar and dry ingredients in one smooth batter with none of the lumping or separating that cold butter causes in an unheated British kitchen in winter. Use any oil with no smell of its own — sunflower, a light rapeseed, a mild vegetable oil — because a strong olive oil will fight the lemon zest instead of carrying it.

Caster sugar, not granulated, matters more here than in a butter cake: it dissolves into the oil-and-flour mixture rather than sitting as grit, since there's no creaming stage to work it in mechanically. Lemon zest only — never the juice — because juice adds acid and liquid that unbalance a batter already carrying no yolks to buffer it; zest gives scent without touching the chemistry.

On baking powder: 16 g sounds like a lot against 100 g flour, and some say — no, because the egg whites are already lifting the cake, so this is just belt-and-braces. Partly true. But the whipped whites lift what's already in the tin; the baking powder keeps lifting as the structure sets in the oven's heat, when the whites' trapped air is starting to expand and could easily escape before the crumb firms up. Skip it and you get a cake that rises in the oven and deflates on the counter.

On the tin: a ring shape isn't decoration, it's function — the hole means no part of the batter is ever more than a couple of centimetres from a hot surface, so a cake this light cooks through evenly without a dense, wet centre. In a British kitchen without a proper ciambella tin, a bundt tin does the same job; if all you have is a round tin, stand an oven-proof glass or ramekin in the middle, which fakes the same geometry. Greasing and flouring (or the damp paper trick) isn't fussiness — it stops the cake tearing itself apart against the tin's sides when it shrinks slightly on cooling, since this crumb has nothing fatty enough to release cleanly on its own.

180°C means a domestic oven running at a true, settled 180 — if yours runs hot or has no fan, that's the one variable you adjust by watching, not by the clock. Thirty minutes is where to start checking, not where to stop: push a skewer into the thickest part of the ring, and if it comes out with wet batter clinging, it goes back in. A skewer with a few moist crumbs, not wet batter, is done — crumbs mean it's set; wet batter means the structure hasn't finished cooking.

And the patience is in the cooling, not the baking. Cut it warm and the crumb, barely held together by whipped egg white, will crush under the knife and taste gummy in the centre even if it's fully baked — it needs to sit and firm up as it cools, same as a soufflé needs to be left alone. Icing sugar goes on only once it's properly cold, otherwise it melts into the surface instead of sitting as a dusting. Eight slices, built for a pot of tea with milk rather than a pudding course after the Sunday roast — it's not a cake that needs an occasion.