Preheat oven to 175 degrees Celsius. Grease 2 9-inch baking tins and line the bottom with parchment paper. Set aside.
In a large mixing bowl measure the unsalted butter, caster sugar and brown sugar. Sift in all-purpose flour, cocoa powder, baking soda, baking powder and salt. Add in vanilla extract and milk. Using an electric mixer, mix the mixture on low for 1 minute, then turn the speed up to high and beat for 2 minutes.
Add in the 2 eggs and continue to beat on high for another minute.
Divide the batter between the tins and bang the tins twice each on the table counter to release excess air bubbles. Bake for 20 to 25 minutes until a skewer inserted into the centre comes out clean.
Let the cake cool completely before cutting them into rounds.
Cream
Sprinkle gelatin all over the strawberry purée. Set aside for at least 5 minutes.
Whisk egg yolks and sugar in a small mixing bowl until pale and thick. Set aside.
Place the milk in a medium pot and bring to a simmer or until small bubbles begin to appear on the edges of the pot.
Temper the egg yolks with the hot milk. Transfer the egg yolks mixture back into the pot and continue to cook the custard over medium-low heat, stirring constantly with a wooden spoon until thickened.
Turn the heat down to low and add in the strawberry-gelatin mix. Stir until the gelatin has dissolved fully. Remove from heat and strain the mixture to remove any lumps. Stir in the lemon juice and set aside to let the mixture cool to room temperature, stirring occasionally.
Whip the cream until medium stiff peaks formed. Whisk in 1/3 of the cream into the strawberry mixture to lighten it, then fold in the remaining whipped cream. Use the cream immediately.
Assembly
Cut the chocolate cake layers into 8-inch rounds. Place one round in a 8-inch ring mould (3-inch in height). Pour 1/2 of the Bavarian cream over the cake layer. Place the other cake layer on top and pour in the remaining Bavarian cream. Refrigerate for at least 4 hours until the cream layer is firm.
Wrap a hot towel around the sides of the cake and unmould the cake. Transfer the cake onto a serving dish.
Cut a piece of parchment paper or plastic sheet such that it wraps around the cake and is of the same height as the cake (or a little taller). Spread white chocolate over the parchment paper and let the white chocolate set a little. Wrap the white chocolate collar around the cake and refrigerate until the collar is fully set. Peel off the parchment paper.
Decorate with strawberries and dust generously with icing sugar and serve!