Preheat your oven to 170 degrees Celsius. Grease and flour a 9-inch square cake tin.

In a large mixing bowl, cream together 360 g of butter and 360 g of granulated sugar for 2 minutes until light and fluffy.

Add the eggs two at a time to the creamed mixture, beating well after each addition.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt. Sift this dry mixture into the butter and sugar blend, alternating with the milk.

Pour the batter into the prepared tin and bake for 45 to 50 minutes. Check for doneness with a skewer.

Cool the cake in the tin for 2-3 minutes, then flip onto a wire rack to cool completely.

Cream 400 g of softened salted butter until smooth.

Gradually add 800 g of sifted powdered sugar, mixing until combined.

Fold in 1.25 teaspoons of vanilla extract and milk if needed.

Knead 1 tablespoon of CMC powder into 250 g of orange fondant. Cut into 10 cm lengths to create witches' legs.

Roll the black fondant into thin strips and attach to the orange legs for stripes.

Shape black fondant into small balls for shoes and attach to the ends of the orange legs.

Level the cooled cake and cut into 18 circles using a 3-inch cutter.

In each jar, layer a teaspoon of sprinkles, followed by a cake circle and buttercream. Repeat for a second layer.

Insert fondant witches' legs into the jars for decoration.