Tiramisu recipes are precise about everything that does not decide the outcome. Grams of mascarpone, number of yolks, size of dish, brand of cocoa, all specified to the decimal, and then the step that separates a clean-cut slice from a tray of sludge gets one word: "dip". How long, in what, at what temperature, silence. The dish's most common failures, soggy and dry, both live inside that one word, and both are fixable with a count you can say out loud.
Dip each ladyfinger for about one second per side, two seconds total, in strong coffee that has cooled to room temperature, and assemble while every biscuit still has a dry core. Then refrigerate the finished dish for at least six hours, because the rest is where the ladyfingers actually finish soaking, from the inside out. Soggy tiramisu is a long dip or a hot dip. Dry tiramisu is a skipped rest, or the wrong biscuit. The dip is not the soak. The rest is the soak.
What to do
Brew around 250 to 300 ml of strong coffee for a standard dish of about 24 savoiardi. A moka pot's small, concentrated, bitter-leaning brew is exactly right here, and so are a few espresso shots topped up with a little water. With a filter brewer, start from the standard sixty grams per litre and double the dose, because the mascarpone will mute anything weaker. Let it cool completely. Sugar in the coffee is a taste call; the mascarpone layer is already carrying plenty.
Then dip, one biscuit at a time, flat side down, one second, turn, one second, out. Lay it straight into the dish. Do not queue dipped biscuits on a plate, and never pour coffee over an assembled layer to top it up.
How to check your count
Calibrate on a sacrificial biscuit before you commit the batch. Dip it at your count, then cut it in half. You want a wet ring around a pale dry core about the width of a pencil. That dry core is not a mistake. It is the buffer that will absorb moisture during the rest, and it is the difference between a slice that stands and a layer that flows. If the core is already gone at the cutting board, your count is too long or your coffee is too warm. If the wet ring is barely a skin, add half a second per side and cut again.
Brands differ, so this thirty-second test is worth doing once per box. A dense, hard savoiardi takes a fraction longer than an airy one, and the test tells you which you have without guessing.
Why it works
A savoiardi is a sponge biscuit baked dry on purpose. Its open crumb pulls liquid in by capillary action, the way a paper towel does, which is why the absorption you can see happens in seconds rather than minutes. The wicking does not stop when the biscuit leaves the coffee. Whatever soaked into the outer ring keeps migrating inward for hours, and the biscuit also draws moisture out of the mascarpone cream it sits against. That slow redistribution is the actual soak, and it is why the dish is assembled in a state that looks underdone and then rested. Six hours is the working minimum. Overnight is better, and the dish cuts best on day two.
Temperature earns its place in the rule because liquids thin as they warm, and thinner liquids wick faster. In hot coffee the difference between one second and three is the difference between structure and pulp, a margin nobody can hit reliably while assembling two dozen biscuits. Room-temperature coffee widens that margin to something a human can work with. A warm dip also softens the biscuit's surface enough to slump under the weight of the cream, and it warms the layer that the mascarpone, a fat-based cream that softens quickly above fridge temperature, is about to be spread against.
The published recipes are no help on any of this. Alan's Unofficial AeroPress Recipe Book (2020) has you lay the ladyfingers on a baking sheet, pour the coffee and rum mixture over them, and "allow to soak", with no time given, which produces pulp at one end of the tray and dry biscuits at the other. Hatfield's The Coffee Cookbook (2016) says "dunk", full stop. Across four tiramisu recipes in the popular coffee cookbook tier we analysed, not one states a soak time. The single variable that decides the dish is the one the genre leaves out.
What this will not do
The count is written for savoiardi and does not transfer to soft, cake-style sponge fingers, which have a moist closed crumb that first resists the coffee and then squashes; no timing rescues them, so buy the hard ones. It will not fix a filling that pours: a loose mascarpone layer is a warm or over-beaten mascarpone problem, upstream of the coffee entirely. It will not rescue a tiramisu that is already soggy, because the moisture that migrated in cannot be coaxed back out. And it will not remove the caffeine, which survives assembly intact: a dish soaked in 300 ml of strong coffee is a genuinely caffeinated dessert, worth remembering when it is served at eleven at night or cut into slices for children.
How you know it worked
The test is the first cut after the rest. A slice should come out with a clean layered edge, the ladyfinger band uniformly darkened and tender all the way through, no pale dry patches and no crunch. The floor of the dish should be dry: pooled coffee under the bottom layer means the dip ran long, and a slice that slumps toward the plate within a minute means the same thing. Distinct crunchy biscuit in the middle of a rested slice means the dip was too short, or the rest was cut to two hours because dinner ran early.
When you are unsure at assembly time, err dry. A rested tiramisu forgives a slightly timid dip, because the mascarpone keeps feeding moisture to the biscuits overnight. Nothing forgives a generous one.