Grease a deep 23cm cake tin and line the base with greaseproof paper.
Place the butter, white chocolate, milk and vanilla extract in a small saucepan, then heat gently, stirring, until melted.
Combine the flour, bicarb and sugar in a large bowl with a pinch of salt, then stir in the melted ingredients and eggs until smooth.
Pour the batter into the tin, then bake for 1 hr, or until the cake is golden and a skewer inserted into the centre comes out clean. Cool in the tin. Once cool, the cake can be wrapped in cling film and foil, then frozen for up to 1 month.
To make the frosting, beat together the Philadelphia, butter and icing sugar until smooth.
Spread over the cake, then decorate with mini eggs.