1 envelope powdered unflavored gelatin (measure it to make sure it's 7 grams by weight, or 2 teaspoons)
9 ounces cold water (that's 1 cup + 2 tablespoons)
9 ounces evaporated milk (the stuff in cans; not sweetened condensed milk)
3 ounces heavy cream
1 tablespoon instant coffee, or more to taste
3 tablespoons sugar, or more to taste
1 medium banana
A cute jello mold is nice (silicone is easiest), but a wide, flat bowl or even a baking dish works fine as a mold. Or chill in individual molds or bowls.
Measure your gelatin, and make sure you have 7 grams or 2 teaspoons of the stuff. I know I already mentioned this in the ingredients. Just make sure you do it, because they have a habit of filling the envelopes inconsistently.
Pour about half the water into a large bowl, and sprinkle in the gelatin; it'll clump if you just dump it in. You can whisk it out if that happens, but then you'd have to smell it. You don't really want to smell it. For a tasteless, odorless thing, gelatin has a habit of being rather animal-smelling when it hits water at first. Give the mixture a stir or two to get all the powder hydrating and "blooming."
Heat evaporated milk, remaining water, sugar and a pinch of salt over moderate heat, stirring constantly. I like to use a heat-proof rubber spatula, making sure to get all the sides and the bottom. Keep heating and stirring until a pale froth of tiny bubbles coats the surface, and the liquid trembles as if afraid when the spatula moves through it. It should be steaming fairly vigorously, and there may be tiny bubbles threatening to boil around the edges.
Take the milk mixture off the heat and stir in the instant coffee. The reason not to heat the coffee in the milk directly is that coffee that reaches the boiling point can release a substance that can actually destroy gelatin. Black magic!
Stir the hot coffee milk into the bloomed gelatin. Adjust with sugar and coffee to taste, remembering that sugar tastes less intense in cold things, so you may want to sweeten it just a little beyond what you think tastes perfect.
Whisk in heavy cream, and whisk it in good, for a few solid seconds. You'll kick up some froth, but don't worry about it.
Let cool to room temperature. If there's still froth from the whisking floating, use your spatula to gather and smear it against the sides of the bowl to pop all the bubbles.
Slice banana into Â¼-inch coins, stir them into the cooled coffee mixture and pour into mold. If you want to be fancy, lay the bananas down decoratively at the bottom of your mold, pour in a very thin layer of the pudding and chill in the freezer until set, then gently pour in the rest over the back of a spoon. (Otherwise, the bananas will float all willy-nilly.) Wrap tightly in plastic, and chill at least 4 hours.
Serve straight from the mold or turned out onto a dish (careful!). For help turning it out, run a thin knife around the edges. If it still doesn't want to come out quickly, dip the whole mold in hot water for a few seconds, turn the dessert out, and then chill again in fridge for 20 minutes before serving. Best served within a day, but will keep for several.
Francis Lam is Features Editor at Gilt Taste, provides color commentary for the Cooking Channel show Food(ography), and tweets at @francis_lam.