Preheat oven to 350°F / 180°C and spray brownie bites pan lightly with cooking spray (if you aren't using the brownie bites pan, see post above for what to use instead)
Sieve all the dry ingredients for the cake into a bowl
Add the egg, vegetable oil, milk and vanilla and stir until everything is smooth and combined
Add the hot water and mix in - the batter will be very liquid
Pour the batter into the brownie pan, fill the cavities about ¾ full
Bake for 15 minutes or until a skewer inserted comes out clean
Allow to cool in the pan for about 30 minutes before trying to remove
Make the Caramel
Put the sugar and water in a saucepan over a medium-low heat
Don't stir the sugar, just let it melt and dissolve into the water, once it has totally dissolved, keep stirring until it starts to turn a light amber colour, then add the butter
Once the butter has totally melted, keep cooking, stirring constantly for about a minute
Slowly pour in the cream, stirring constantly - the mixture will bubble up and might spit a little, so be careful
Once the cream is totally incorporated, check the colour of your caramel, if you are happy with the colour, remove from the heat, if you want it darker, keep going until it is how you like it - don't leave it unattended though as it can burn very quickly!
Allow it to cool and thicken a little before trying to put into the chocolate squares - use a spoon or piping bag to put a small amount on there, just until it fills up, then gently tap the square on your worktop to tease it into the corners