Heat your oven to 350°F and grease and cover pans with parchment paper.
Using a stand mixer, beat the butter, sugar, and vanilla for 5-6 minutes, until pale and creamy. Then add the eggs until well-combined.
In another bowl, mix the flour and baking powder. Then, fold it into the stand mixer bowl and mix on low until incorporated.
Divide the mix into two pans and bake for 25-30 minutes until golden and springy and a skewer comes out clean. Cool them in their pans for 5 minutes, and then turn them onto a wire rack carefully to cool completely.
For the buttercream, beat room temp butter, confectioners' sugar, and vanilla on medium speed for 1-2 minutes until fluffy.
Then, spread the jam evenly on one of the cake halves. Fill a piping bag with buttercream, and snip a ½-inch hole into the bag. Pipe the buttercream in little blobs around the cake, or just spread it on with a spatula.
Carefully place the second sponge on top and press together. Dust with confectioners' sugar and garnish with fresh strawberries.
Notes
This cake is even more delicious with homemade jam! I hope to make my own from scratch one day, but until then, I highly recommend the Comte de France brand of strawberry jam.