Preheat the oven to 355°F (180°C).

Mix the milk with the vinegar and let it sit to sour for about 10 to 15 minutes. 

Prepare two 8-inch (20-cm) round springform pans. Grease them lightly and cover the bottom with parchment paper. 

Sift all the dry ingredients into a large bowl. In a smaller bowl, mix the oil and lemon juice and pour the mixture into the dry ingredients. Using a silicone spatula or a large wooden spoon, mix gently and add the soured milk gradually. You will get a fluffy, smooth batter. 

Divide the batter equally between the two prepared springform pans. Shake them to level and tap gently a few times on the countertop so the bubbles are settled. 

Put the pans in the oven, and bake the cakes for 25 minutes. After the time has elapsed, test if they’re done with a toothpick. Insert it into the cakes, piercing it all the way to the bottom. If it comes out clean, with just a few crumbs on it, the cakes are done. If there’s any batter on it, bake the cakes for another 5 minutes and test again. If the toothpick is still a little wet, leave it for another 5 minutes in the hot oven with the heat off. 

Transfer the cake pans to a cooling rack and leave them to cool for about 10 minutes. When they’re cool enough to be taken out of the pan, turn the cakes over on the cooling rack. Remove the paper. Leave the cakes to cool upside down so the tops flatten. 

When the cakes are completely cooled down, place the jam in a small pot and warm it over a low flame, stirring until smooth. Turn the bottom cake upside down to get an even surface on top so the cakes will neatly stack. Alternatively, use a knife to cut the tops of the cakes to level them. Brush the top of both cake halves with the jam and place one on top of the other. Brush the sides and top with the jam as well.

To prepare the glaze, melt the cocoa butter in a double boiler, then add the syrup and stir until combined. Add the cocoa and keep stirring until smooth. Remove it from the boiler and add the milk, whisking continuously until smooth.

Apply the glaze to the cake using a spatula. Glaze the sides and top of the cake, and smooth it out as best as you can. Place the cake in the refrigerator to firm up.

Remove the cake from the refrigerator at least half an hour before serving, so both the sponge and the glaze soften. If you’re letting the cake rest for a day or more before serving, keep it in the refrigerator in an airtight container to avoid drying out the cake. It will keep for up to 10 days.