Preheat the oven to 190C/375F and line two 20cm springform baking tins with baking paper.
Using an electric mixer, beat the butter and caster sugar until pale and fluffy, about 3 minutes.
Add each egg one at a time, ensuring it's well incorporated before adding the next one. Add the vanilla extract.
Sift the flour and baking powder twice and then add that to the cake batter while mixing on low. Add the milk and briefly whisk to combine. Do not over mix.
Scrape down the bowl of the mixer and divide the batter evenly between the 2 cake tins. Even the top out with a spatula.
Bake for 20 – 25 minutes until golden brown and springy to the touch. The cake is done when you insert a sharp knife into the middle and it comes out clean. If necessary and to prevent over-browning, loosely cover the cakes from about 10 minutes into the baking time.
Cool on a rack.
Make the icing by whisking all the ingredients until pale and fluffy.
Assemble the cake starting with a layer of icing then a layer of Bonne Maman jam. Place the second layer on top and dust with icing sugar.