Preheat the oven to 190oc/170oc fan and grease and line two 20cm sandwich tins. In the bowl of a stand mixer, or large bowl if using a handheld whisk, beat together the butter and sugar for around 3 to 4 minutes until pale and fluffy.
Add the eggs one at a time, beating well after each addition until fully incorporated. The cake batter may look a little split, but the dry ingredients will bring it back together. Add the flour and baking powder and beat together until smooth. Add the milk a little at a time until the cake mix is light and fluffy and at a dropping consistency.
Divide the batter between the two prepared tins and bake for 20 to 25 minutes until golden and a skewer inserted in the middle comes out clean. Cool for 5 minutes in the tin then remove the cakes and leave to cool on a wire rack completely.
To make the buttercream, add the butter to the bowl of a stand mixer or large bowl if using a handheld whisk. Beat for around 5 minutes, scraping the bowl to ensure all of the butter is being whipped. Once the butter is very pale, add half the icing sugar and beat to a smooth icing. Add the second half of the icing sugar and beat again until the icing is an off-white colour and smooth. Add the vanilla and a little milk to loosen and beat again until the buttercream is soft and pipeable.
To assemble, place one of the cakes upside down on a cake stand or plate. Briefly mix together the jam in a small bowl to loosen then spread over the first cake. Scoop the buttercream into a piping bag fitted with a round nozzle and pipe small blobs around the edge of the cake, following the pattern into the middle of the cake until it is covered in buttercream. Alternatively, spread the buttercream over the jam with a palette knife for a rustic look. Place the second cake upside down on top of the buttercream then dust with icing sugar to finish.
Recipe by Victoria Sponge Pease Pudding at http://victoriaspongepeasepudding.com/baking/classic-victoria-sponge-with-jam-and-buttercream/