1teaspoon(1teaspoon)baking powder(ensure gluten-free if necessary)
¼teaspoon(¼teaspoon)bicarbonate of soda (baking soda)
For the filling:
Mix together all the ingredients in a small bowl, ensuring everything has been mixed together properly.
Place in the fridge for around 20 minutes until hardened.
For the cake:
Preheat oven to 180 degrees Celsius (350 degrees Fahrenheit).
Place the coconut oil in a bowl and melt over a saucepan of boiling water or in the microwave (skip this step if using any other oil).
Once melted, add the milk to the same bowl along with the vinegar, maple syrup, vanilla, salt and ground almonds.
Sift in the flour, baking powder, bicarbonate of soda and cocoa powder.
Mix well, adding a tiny splash more milk if it’s looking too dry.
Lightly grease a small pudding tin (I used one measuring 8cm/3 ¼ inch on top, 5.5cm/2 ¼ inch on the bottom with a height of 5.5cm/2 ¼ inch).
Place about ¼ teaspoon cocoa powder in the tin and move it around so that all the inside of the tin is coated in the cocoa powder - this will make it easier to remove afterwards.
Place half of the cake batter in the tin and make a small well in the centre.
Remove the filling from the fridge and use your hands to roll it into a slightly flattened ball.
Place the ball into the well in the centre of the batter in the tin, making sure that the ball isn’t touching the sides of the tin.
Cover with the remaining cake batter, ensuring that the sides of the ball are well covered with cake batter, as well as the top.
Bake in the oven for around 20 minutes until risen - it's difficult to check whether it's done using an inserted skewer, but 20 minutes of baking works for a tin of this size - you can use a tin of a different size, but you will have to adjust the cooking time accordingly depending on the size and shape of your pudding tin.
To make the cake more stable once turned upside down on a plate, carefully slice off the slightly curved top surface of the cake.
Put a place upside down over the top of the pudding tin then quickly flip it over and remove the tin so that the cake is turned upside down on the plate.
The vinegar is crucial as it's acidic, which means it reacts with the alkali bicarbonate of soda (baking soda) to create a bubbly batter and fluffy sponge. If you don't have vinegar, replace it with lemon juice.
Greasing the tin and dusting it with cocoa powder is essential for making the cake easy to extract afterwards.
Make sure that the filling has been in the fridge for around 20 minutes before putting it in the centre of the cake batter.
Make sure to put the ball of filling in the centre and that the sides are covered properly - otherwise the filling will seep out.