Preheat your oven to 170°C (340°F) and prepare a 9-inch square cake tin by greasing and flouring it.

In a large mixing bowl, cream together softened butter and granulated sugar until light and fluffy, about 4-5 minutes.

Add the eggs one at a time, mixing well after each addition. Sift together self-raising flour, black cocoa powder, baking powder, and salt, then alternate adding this dry mix with the milk, folding in the vanilla extract at the end.

Pour the batter into the prepared tin, smoothing the top with a spatula. Bake for 45-50 minutes or until a toothpick inserted comes out clean.

Allow the cake to cool completely in the tin on a wire rack.

While the cake cools, whip the softened butter in a mixing bowl until smooth and creamy.

Gradually add sifted powdered sugar, mixing with a spatula first, then using a mixer to incorporate air for lightness.

Blend in vanilla extract and electric green food coloring until vibrant and easy to pipe.

Level the top of the cooled cake with a serrated knife and cut out 9 circles.

Begin layering by adding Halloween-themed sprinkles at the bottom of each jar, followed by a cake circle, then a layer of green buttercream. Repeat until jars are filled, finishing with buttercream swirl and festive toppings.

Roll out orange fondant and shape into whimsical witch legs, using black fondant for the shoes and adding details as desired.

Insert each fondant witch leg into the assembled jars for a charming decoration.