Pre-heat oven: 180°C / 160°C (fan) / Gas Mark 4 / 350°F
Cream together the butter and sugar until pale and smooth, then beat in the egg until fully combined.
Sieve in the flour and baking powder, folding in gently. Then stir in the vanilla extract and milk until only just combined.
Pour the cake batter into a greased and lined 8-inch round cake tin and bake for 20-25mins until springy to touch and a skewer comes out clean.
Allow the cake to cool in the tin for 15mins before removing and transferring to a wire rack to finish cooling while you make the buttercream.
Buttercream for filling:
Beat the butter (either by hand, using an electric mixer or stand mixer) until pale, light and fluffy.
Sieve half of the icing sugar into the butter and beat until combined, then repeat this with the remaining half of the icing sugar.
Add in the milk and vanilla extract, mixing until only just smooth.
Cake pop filling:
Crumble up your cooled sponge into a large bowl, either using your hands or a fork.
Using a fork or spatula, thoroughly mix in the buttercream to the crumbled cake. Your cake pop filling should be able to hold together like a soft dough.
Scoop a walnut-sized amount of the filling mix (using a tablespoon or cookie scoop) and roll it in your hands to make a round ball. Place on a flat plate or tray lined with greaseproof paper.
Repeat the above step until you've used up all of your filling mix and refrigerate for 1hr.
Cake pop assembly:
In a narrow heatproof jug, mug or other container, slowly melt the candy melts in the microwave for 20secs at a time, stirring between bouts until smooth, then stir in the oil until you have a melted chocolate consistency.
Take 4 cake balls from the fridge and dip one end of a lollipop stick into the melted candy before pushing it halfway into a cake ball. Repeat for all 4 cake balls.
Holding the stick, dip a cake ball into the melted candy, covering it completely. Gently tap off any excess back into the container before topping with sprinkles and placing into a holder (e.g. cake pop stand or styrofoam block).
Repeat the above steps until you've turned all the cake balls into cake pops. Allow the candy coatings to set for 5-10mins at room temperature, then enjoy!
* If you don't have an 8-inch round cake tin, you can instead use a 6-inch round cake tin and bake your sponge for 25-30mins instead.** You can swap the plain flour in this recipe for self-raising flour of the same quantity and exclude the baking powder.