Yes, cola. It makes a cocoa cake improbably light.
About 45 minutes from starting to sitting down, and it is straightforward. Most of that is active, so read the method through before you start rather than chopping as you go.
Into a tin straight away, don't let it sit.
Use 120ml evaporated milk simmered with 100g sugar until thick.
You can prepare it a few hours ahead and reheat gently. It keeps two days in the fridge, though it is best on the day.
Yes, it is vegetarian. It is not vegan as written because it contains dairy; swap the dairy for a plant alternative and the rest of the method is unchanged.
Yes, this one needs an oven. If you do not have one, look at the no-oven filter on the baking page: eleven of the bakes here are built for a cooker, a pan or the fridge.
On its own, warm, with tea or coffee. Baking is chemistry, so scale it by weight rather than by eye: double every quantity, use a tin with roughly double the area, and expect to add ten minutes or so. Judge it by the skewer, not the clock.