Preheat the oven to 180 º C.
Add the lemon juice to the milk and mix. Set aside for about 10 minutes.
In a bowl, whisk the milk, eggs, and olive oil together.
In a separate bowl, mix the flour, cocoa powder, sugar, baking powder, baking soda, and salt.
Slowly add the mixture of dry ingredients to the wet ones, mixing until well incorporated.
Finally, pour in the hot coffee, folding it into the mix carefully with a spatula. The cake batter should be a bit liquid, so don't be alarmed as this is normal consistency.
Pour the mix into a heart-shaped cake pan, previously greased.
Bake for about 40 minutes, or until a skewer inserted in the center of the cake comes out dry. Let it cool down a little and remove the cake from the pan to the serving plate.