Preheat the oven to 180°C (350°F). Line an 18 cm cake pan with baking paper.
In a mixing bowl, beat the eggs and sugar with a mixer for 3 to 4 minutes, until the mixture becomes lighter in color and foamy.
Add the oil and milk and mix briefly.
Add the sifted flour and mix until combined.
Pour the batter into the prepared cake pan and bake for 12 to 15 minutes, or until lightly golden. Let the cake cool completely.
To make the filling, briefly beat the mascarpone cheese and powdered sugar until combined.
Add the cold heavy whipping cream and continue beating until the filling becomes firm. Do not overwhip.
Divide the filling into 2 equal parts.
To make the ganache layer, heat the heavy cream until it comes to a boil. Pour it over the chopped milk chocolate. Let it sit briefly, then stir until smooth. Allow it to cool slightly.
Soak the cooled cake base with 50 ml milk.
Spread the first half of the filling over the cake base.
Place the cake in the freezer for 10 minutes.
Pour the ganache layer over the filling and spread gently.
Return the cake to the freezer for another 10 minutes.
Spread the second half of the filling over the ganache layer.
Refrigerate the cake for 1 to 2 hours.
To make the topping, heat the heavy cream until it comes to a boil. Pour it over the chopped milk chocolate and stir until smooth.
Pour the topping over the chilled cake and smooth the surface.
Refrigerate for another 2 hours before slicing and serving.