I improvised a cake, and it turned out to be the greatest cake in the world. This is not that cake, because I didn’t write down the measures at the time. In a few tries I did come up with a pretty great recipe nonetheless. It’s easily adaptable for different flavours, so here is the cake recipe as well as some variations.
one very ripe banana 
50g sunflower or coconut oil
100-120g oat milk 
250 g plain flour (all-purpose flour)
8g baking powder
120 g sugar (any kind) 
pinch of salt
Mash the banana well with a fork, so that most of the lumps are gone. Mix it with the rest of the wet ingredients (if your banana and oil separate, it might help to use a whisk). Use only 100g of the oat milk, the rest is only there in case the batter is too dry.
In a separate bowl, add the dry ingredients. Make sure you break up any clumps in the baking powder with a sieve of with your fingers. Mix them well.
Preheat the over to 180°C (fan oven, probably 200°C otherwise). Prepare your cake form: I prefer to line it with baking paper, for guaranteed and easy removal of the whole cake, but you could also grease it with some oil.
When the oven is (almost) ready, combine the wet and dry ingredients. Mix only as much as needed to hydrate all the flour . If it’s too dry, add a bit more oat milk. Poor the batter in your cake form. Spread it out with a spoon or spatula, and shake the form a bit to get rid of any trapped air.
Bake your cake for 35-40 minutes. At the 35m mark, you may test whether the cake is ready by inserting a skewer or knife. If it still has wet batter on it, bake for a few more minutes. Let the cake rest for at least 15 minutes before eating (don’t worry it will still be warm). Letting it cool completely is also fine, of course.
 No banana is too ripe for cake, you don’t have to cut out the brown parts either. As long as it’s not rotten or mouldy, you’re good 🙂 You can also freeze a banana for future cake making (defrost it in the microwave or with a lot of patience).
 I’ve only used oat, but I don’t see any reason why soy, rice, almond etc wouldn’t work just as well.
 You can adjust the sweetness of your cake by using more or less sugar. This recipe makes a reasonably, but not overly sweet cake (less sweet than most store-bought cakes). You may also want to adjust it for the type of sugar you are using (some are less sweet), and for any add-ins that carry additional sugars, such as dried fruits.
 The reason for mixing wet and dry ingredients separately, as well as minimizing the mixing, is to preserve the fluffiness of the cake. Baking powder has an acidic and an alkaline ingredient. When the powder hydrates, these components react and form small bubbles of gas (CO2) in the batter; this leavens the cake. Batter that sits for too long after the baking powder is activated, or that is over-mixed, looses its bubbles and will produce a less fluffy cake.
Cake… but with banana on top
Slice two bananas length-wise so that you create two mirrored halves (i.e. two halves that can lie flat). Before putting your cake in the oven, press the banana halves lightly into the top of your cake, cut-side up. Main purpose: it looks fancy.
A simple way to add some flavour and warmth to your cake is to mix in some spices. Add them in with the dry ingredients. Whisking after is recommended to ensure the spices will be distributed evenly throughout the dough. This option also works well in combination with banana or apple slices on top, or with pieces of apple in the batter.
You can add whatever spices you like, but cinnamon is a must. And don’t be stingy with it, one teaspoons for this recipe seems about right. You could also add (about 1/4 tsp) cardamon, kurkuma, ginger, and/or (about 1/8 tsp) ground cloves and nutmeg. Of course, you could also use pre-mixed cookie spices 🙂
Good ol’ marbled chocolate
This is a thing in the world of cake, isn’t it? I don’t think it’s that impressive flavour-wise, but it does look cool.
Because we need to keep our wet and dry ingredients separate, and split the batter in two, we’ll need four bowls. With one half of the dry ingredients, mix in some cocoa powder (not sure how much exactly, I think about two tablespoons will be enough). When you’re ready, mix the two batters and poor them in side-by-side into the cake form. You can mix them a bit in the form, or poor them in smaller, separate layers, if you want more intricate patterns.
For a full-on chocolate cake, you don’t have to bother with two batters. Just add more cocoa powder and maybe mix in some chocolate chips.
The technical challenge: cake-tatin
In theory, you could make some caramel (suger, water, maybe some vegan butter) and poor it into the bottom of your cake form. Then, you can layer in some sliced apples, before pouring the cake batter on top. If you are patient enough to wait for the cake to cool down completely, there might be a caramel layer on top. It might also be too liquid and soak into the cake, which is still delicious.
All nice things to add into your cake. It’s quite a dense batter, so it should be fine to fold mix-ins in at the end (without finding them all sunk to the bottom of your cake after baking). Having some of the mix-ins on top of your cake generally also looks good. (By the way, this is generally the thing to do for pastry making, as it helps whoever is choosing and/or eating the product to identify the flavour. For example, chocolate chips on top promise chocolate flavour within. This is especially relevant for allergens like nuts. Of course, this assumes one is sharing ones baked goods…)
- Fresh blueberries (These may be too delicate to mix in the batter. I would pour half the batter into the cake form, add half the berries, then the rest of the batter, and the rest of the berries on top.)
- Mixed nuts and dried apricots
- Apple pieces with a spiced batter
- Walnuts and chocolate chips