You will also really struggle to colour the icing unless you get gel food colouring - I bought ours from ebay and paid about £2.50 each, but they last a long time and will save you money if you use it all as you need such a small amount compared to liquid food colouring.
The cake mix we used was your basic sponge. Using classic sponge is tastier. It's a little harder to work with and doesn't last as long, but I'd rather make something that tastes delicious, rather than using a 'construction cake' recipe. You will need to make 3 sponges. 2 round (or square and cut them like I did), and 1 hemisphere.
Ingredients (per cake)
Weigh the eggs, get the same quantity of Sugar, Butter and Self-Raising Flour (it'll be somewhere around 180grams)
Teaspoon Vanilla Essence
Preheat the oven to 160c/320f/Gas Mark 3
Grease your pans and line the flat tins if you wish
Cream together the Butter and Sugar
Add the Eggs bit by bit, mixing in between
Add the Vanilla Essence
Add the Flour
Cook for around 25-30 minutes for a flat cake, 50-55 minutes for a hemisphere cake. Stab it with a skewer to test - if it comes out clean then it's done. If the top starts to burn cover it loosely with foil.
Putting together the design
The 3 Cakes
Ready to roll Icing, or make your own with icing sugar
Blue, yellow and black Food Colouring
Butter and Icing Sugar mixed together to make Buttercream
Take the 3 cakes and pile them on top of each other. Cut them to shape as below. Mine are different colours as I ran out of white sugar and changed to brown!
I was a bit over-generous, you only need a thin layer of buttercream so that the icing sticks. You can use apricot jam instead if you wish.
Make your blue icing. You'll need elbow grease to get the colour even throughout. This temporarily adds air, which makes it look slightly lighter than the end result will be.
Roll it out big enough that it'll cover the cakes completely.
Choose which side you want as the front and drape the icing over the top being careful not to pull, stretch and break it. You'll have to cut off the spare icing at the back and smooth it together as best you can. Then place it onto the surface you'll be using. Smooth the surface with clean, warm hands. Don't stretch the icing, give it a bit of love.
Cut out a template from greaseproof paper for the face. The hole in the spacesuit helmet is larger than you might think and wraps around the face. I can't give you an exact dimension because your cake won't be exactly the same size as mine!
We used cocktail sticks to hold it in place, and 'dot' around the template carefully, then use a knife to cut out the gap for the face. If you press the icing slightly with the edge of a knife you can make it seem thicker than it is. Don't forget to draw a line in the blue icing to be the broken chin strap!
Use the same template (or one exactly the same shape and size) to cut out the face from yellow icing. Roll your yellow icing as thin as you dare. Cut 1mm larger than the template all round - just bigger than the template.
Carefully position your face into the gap. If you press it in then it gives the illusion it's further back, and an actual face behind the mask. The buttercream has a little bit of 'give' to it.
My partner also cut out letters freehand to spell boy no.4's name.
Then you have to make the face using black icing. A bottle top (rum) seemed around the right size to cut out the eyes. Use apricot jam mixed with a little warm water to 'glue' the icing onto the iced cake.
Our mouth stretched as we positioned it. You can avoid this by starting at one end, and if it stretches, cut a little off the other end. Once applied, you can't take it back because the black icing stains the yellow icing.
And voila, you have a Benny cake....
The back of our cake isn't incredibly neat, but it wasn't going to be on display for long before it was cut, and our 4 year doesn't care. If I'd had it out for the whole party I'd have smoothed it more.
He thought it was great, and that's what matters most....