• Preheat the oven to 170℃/150℃fan/350℉ and grease and line with baking paper a deepish baking tray 7 x 11 inch.
• Cream the butter and sugar in a bowl until light and fluffy (2 mins).
• Add the egg whites a bit at a time, adding some of the flour so it doesnt curdle. Add the oil and vanilla essence.
• Add the flour, corn flour and baking powder and slowly add the milk until everything is combined but don't over mix.
• Fold in the sprinkles then pour the mixture into the baking tin and spread out evenly.
• Bake in the oven for 10-15 minutes until golden brown and a skewer or knife comes out clean when piercing the centre of the cake. Leave to cool in the tin for 10 minutes before transferring it a wire rack. The best way to remove the cake is to place the wire rack on top of the tray and hold it together, then turn it upside down. Slowly remove the baking paper.

Buttercream

• Using a mixer on a medium setting, add the butter and whisk until creamy. Add the icing sugar and vanilla essence until it looks crumbly. Turn up the setting then slowly add the milk to get a creamy texture. Transfer to a piping with a large nozzle.

Assembling Cake In A Jar

• Using circle cookie cutters, cut holes that are the same width as the jar (the same size as the rim of the jar).
• Place one piece of cake into the base of the jar, then pipe some buttercream on top, being careful not to touch the glass. Add some sprinkles or anything else you want to add. Repeat the process, ending with the buttercream on top with sprinkles. Make sure there is enough room at the top so you can screw the lid on.
• Any leftover sponge can be broken up and used for another rustic-looking cake in a jar. Use the same process as before.