One of the things we tried hard to do with our book is make it easy to get started making tiny foods. Scale is one of the hardest things to get right when you're just starting out. How much frosting should you mix for a single cupcake? It gets easier and easier to eyeball relative amounts the more you work with clay, but it can be a bit frustrating to get the scale right when you're just beginning.
So, we wrote up our ingredients lists as a series of spheres of clay with two size references: a written one (3/8") and a visual one so that you could hold up your clay to the page and quickly see whether you had the right amount. In theory, this system works beautifully. It does rely on one crucial thing: that there are no mistakes! Unfortunately, we're not perfect, and the cupcake recipe has a mistake in the ingredients list. The written amount is correct (3/8" sphere), but the visual amount actually depicts a 5/8" sphere. Thank you to crafty goat for pointing out the mistake!
As you can see from the photo at left, there's a significant difference in size between a sphere with a 5/8" diameter and one with a 3/8" diameter. In real food terms, 5/8" is about the size of a kalamata olive or a small kumquat, while 3/8" is about the size of a fat pea. Volume-wise, the 5/8" sphere is about 4 times larger than the 3/8" sphere.
You can certainly make a much larger cupcake. However, you'll also need to scale up the frosting amounts. And you'll need to increase the baking time to about 25 minutes for a cupcake with a base made from a 5/8" sphere of clay.
If you'd like to try your hand at the cupcake recipe, it's available in full from two great online craft resources: craftster, and Women's Day.