Step 1
Heat the oven to 160c/fan. Line 2 x 4 inch sandwich tins.
Step 2
Cream softened butter, oil and sugar together for 4-5 mins until pale and fluffy.
Step 3
Add in eggs one at a time, beating well between each addition. Add buttermilk with the last egg.
Step 4
Gently fold in flour, Horlicks powder, tea leaves, lemon zest and salt. Stop mixing when all the flour is incorporated - do not overmix!
Step 5
Split batter equally between two cake tins. Bake side by side for 22 minutes until the sponges are risen, golden brown and spring back when lightly pressed.
Step 6
Leave to cool for 5 minutes then turn out onto a rack and peel off the paper. Cool completely before filling.
Step 7
To make your buttercream, beat the butter for 5-10 mins on a high speed. When very pale and fluffy, add the icing sugar gradually, beating on a medium speed. Add salt and flavourings in and beat on high for 2 more mins.
Step 8
Once the cake has cooled, spread buttercream on the bottom layer, making a well with a palette knife for the jam. Sandwich the other sponge layer on top.
Step 9
Spread icing around outside of the cake, adding and spreading little splotches of blackcurrant jam around the sides. Enjoy!