Sieve all the dry ingredients except sugar into a big bowl, then mix well.
Into another bowl, whip egg and sugar with a mixer until soft and fluffy or triples-quadruples in size.
Add oil and dry mixture then mix well. Set aside.
In a saucepan, heat the milk until bubbles appear on the edges of the pan.
Don't let it boil and turn off the heat.
Pour the hot milk into the cake batter gradually 3 times until evenly distributed.
Pour the batter into a 22 cm x 22 cm rectangular tin.
Bake at 175° Celsius for 15-20 minutes.
After baking, let the cake cool in the tin.
In a bowl, bain-marie dark chocolate chips until all melted.
In a small saucepan heat the heavy cream until bubbles appears on the edge of the saucepan. Turn off the heat. Add to melted chocolate chips and stir until well combined.
Remove the chocolate cake from the tin. Put it on a plate upside down so the top is smooth and flat.
Pour the chocolate ganache over the chocolate cake until the cake is evenly covered.
The chocolate cake with ganache is ready to serve.