Molten Chocolate Lava Cake with a Flowing Center

Which chocolate is best for lava cakes?

With six main ingredients, the chocolate carries almost all the flavor. Buy bars rather than chips. Chips often contain stabilizers so they hold their shape in cookies, and they melt thicker and less glossy.

• 60 to 72% bittersweet: the best balance of depth and sweetness for this amount of sugar.
• Semisweet, around 55%: works, but cut the sugar to 3 tablespoons.
• 80% or darker: intense and slightly dry; add 1 extra tablespoon of sugar.
• Milk chocolate: too soft to set a shell at this ratio, so skip it here.

Melt the chocolate and butter together over barely simmering water, with the bowl clear of the water, and stir until smooth. Let the mixture cool for about 3 minutes before it meets the eggs. It should feel warm, not hot, on the back of your wrist. A pinch of espresso powder deepens the chocolate without tasting like coffee.

Why does a molten chocolate lava cake stay liquid inside?

There's no hidden filling. The lava is simply the middle of the batter, taken out of the oven before heat reaches it. High heat sets the eggs at the edges quickly, forming a thin shell, while the core lags behind. At a gentler 350°F the whole cake would cook through at a more even pace and you'd get a small fudgy cake instead.

Whipping the eggs, yolks and sugar until thick and pale traps air, which gives the tops their puff and crack. Fold the warm chocolate in gently so you don't knock that air out, then sift the flour over and fold just until no streaks remain.

Because the center is underbaked on purpose, the eggs inside don't reach a fully cooked temperature. That's fine for most people, but the FDA advises people at higher risk of foodborne illness to avoid undercooked eggs. For those guests, use pasteurized eggs or bake the cakes to the 17 minute stage.

What each minute at 425°F looks like

The gap between molten and fully baked is about three minutes, so learn the visual cues rather than trusting the clock alone. Ovens vary by 25°F or more, and a thermometer on the rack is worth having. At 425°F in 6 ounce ramekins, this is what each minute looks like.

Press the middle gently with a fingertip. It should give like a water balloon while the rim feels firm. If you're baking from the fridge, add 1 to 2 minutes and check again.

Cocoa, not flour: turning the cakes out cleanly

Unmolding looks dramatic but goes smoothly if the ramekins were prepared well. Brush them with soft butter right up to the rim, add a spoonful of cocoa powder, tilt to coat, and tap out the excess. Cocoa releases as well as flour and doesn't leave a pale film on a dark cake.

Once the cakes come out, rest them for 1 minute, no longer. The shell firms slightly in that time. Wait 5 minutes and the center keeps cooking from residual heat.

Run a thin knife around the inside of each ramekin. Set a plate upside down on top, hold both together with a towel, and flip in one quick motion. Tap the bottom of the ramekin twice and lift.

Dust with powdered sugar and serve right away with vanilla ice cream, lightly whipped cream or a few raspberries. The contrast of cold and hot is the point, and the flow slows within a few minutes.

Is it better to fill the ramekins hours ahead?

For a dinner party, yes. It's the easiest way to serve them. Fill the prepared ramekins, cover them and refrigerate for up to 8 hours. Take them straight from the fridge to the hot oven and add 1 to 2 minutes to the bake. Cold batter takes longer to heat through, which works in your favor, since the center stays liquid a little longer.

Don't bake them ahead and reheat. A cake that's already set won't flow again, though a leftover cake warmed for 20 seconds in the microwave is still a very good fudgy dessert.

If you want a make ahead dessert that needs no oven timing at all, a chilled classic tiramisu sets in the fridge the night before, and vanilla crème brûlée can be baked a day early and torched just before serving. Both use the same pantry staples of eggs, sugar and cream.