Grease two 8-inch / 20 cm square cake tins with oil and line the bottoms with parchment paper / baking paper.

Sift flour and baking powder together in a medium bowl and set aside.

Place softened butter in a large bowl and add sugar. Cream together using an electric hand whisk till light and fluffy. It is also possible to use a stand mixer.

Add the eggs one by one, beating for 30 - 45 seconds after each addition.

Add the flour in three separate parts and fold it through using a spatula.

One part of the batter (⅓rd) will be used to make the plain cake and two parts (⅔rd) of the batter will be used to make the chocolate cake.

Divide the mixture into two bowls – one part (~250g) in one bowl for the plain cake and two parts (~500g) in the other bowl for the chocolate batter.

Stir cocoa powder and milk together to form a smooth paste, and then fold it through the larger portion of batter to make a chocolate batter.

Pour the plain batter in one square tin, and the chocolate batter in the other square tin.

Bake the cakes for 20 – 25 mins until a skewer inserted into the centre comes out clean. Let the cakes cool in the pans for 30 minutes, then invert the cakes onto a rack to cool. Peel off the parchment.

Place milk, sugar and butter in a small saucepan and bring to a boil stirring every minute to dissolve the sugar.

Once the mixture has come to a boil, turn heat to low and cook till the mixture reduces to a thick syrup consistency. This will take about 15 – 20 minutes, and the consistency will be similar to condensed milk. Let the mixture cool to room temperature.

Place the cream in a bowl and heat in a microwave in 30 seconds interval. It should be hot with little bubbles at the edges, but not boiling. Add the chopped baking chocolate to the cream and let the chocolate sit in the warm cream for about 5 minutes.

After 5 minutes use a dry spatula to stir the chocolate and cream together till a smooth ganache is formed. Keep the ganache in the fridge for about 20 - 30 minutes so that it firms up and becomes a thick spreadable consistency.

Use a serrated knife to cut off any doming from the top of both the cakes and then cut the chocolate cake in half. Reserve the scraps and turn them into crumbs.

Start assembling the cake by placing one chocolate cake on the bottom. Spread a few tablespoons of the butter icing on top of the cake, and then top with the plain cake. Spread the plain cake with more butter filling, and then top off with the other chocolate cake. Reserve the remaining butter icing.

Wrap the cakes in cling film and keep in the freezer for about 20 – 25 minutes. This will chill the cakes as well as the butter filling.

Remove the cakes from the freezer and unwrap. Use a serrated knife to cut off the edges of the cake to create a straight square edge. Use a pastry brush or a spoon to apply the remaining butter filling to the sides of the cake. Use your hands to carefully apply the crumbs to the sides of the cake. Finally, frost with the chocolate ganache on top, and use a pastry comb to make a design on the cake.

If you want the signature Bombay Bakery chocolate cake look, add a few tablespoons of powdered sugar / icing sugar to the remaining butter filling till it is of piping consistency. Pour the filling in a piping bag or a Ziploc bag, and snip of the top. Pipe one straight line from left to right about ⅓rd of the way from the top of the cake. Pipe another straight line from top to bottom about ⅓rd of the way right of the cake. Place a yellow fondant flower in the intersection of the two lines.