I've seen so many cakes with the little building blocks with letters on them.  Are they cake, fondant, gumpaste, what?  and how do you get them so square and smooth?

AI have done 2 cakes and just did each cube from memory about 25-30grams each. A big waste of fondant but looked very good. I tried putting foil inside and wrapping the foil with fondant but it didnt work. I didn't bother attempting to use cake

I've never done the blocks, but if I was going to, I'd use RCT.  I'd form the blocks out of the RCT, then rub them on a flat surface till they're smooth enough to cover with fondant or gumpaste.  Any small imperfections will show through the fondant, so I'd probably cover them with melted chocolate or candy melts to make sure they're completely smooth before applying the fondant. 

I just did a cake a few days ago with baby blocks.   I made petit fours and outlined them in butter cream.   Not the neatest way to make blocks...but I wanted them to be able to eat them.

I have never made blocks either, but had a thought that you could probably use sugar cubes if you want them tiny..... just a thought.

AI have done it both ways. I've made tiny blocks from fondant as top decor for the main cake. For my baby shower, I made individual blocks. Pain in the ass!! Don't know what I was thinking. Hormones. Each block was 3" x 3". Never do it again ....or really get paid!

ASeriously. Nightmare. Had to come back & add that I did 20 of them. One for each guest & a couple of extras. I remember crying & telling my husband I just wanted to go to Publix & buy cupcakes. I was so exhausted. What was I thinking?!

HI, when i made blocks for a baby shower, i used blocks of styrofoam and covered and decorated in fondant, etc. The recepient kept the blocks. I have used cake before, but was hard to do and did not turn out as good as using the styrofoam blocks. hth

I actually just uploaded a cake where I made baby blocks. I pre-cut squares out of fondant with some tylose mixed in and let them dry. Then, I made my blocks out of Rice Krispies treats, covered them in buttercream and stuck the pre-cut squares to the blocks. I used fondant to decorate and trim the blocks to hide the seams. I did take me longer than I expected, though.

Inspired by Michelle has a video tutorial about making them from fondant.

I cut out individual squares from gumpaste and let them get hard. Then I glued them together with the same color of melted chocolate. Before gluing on the last panel, go into the inside part of the cube and add more chocolate to reinforce them. This makes a lightweight, hollow cube.

Great idea Dora!

You may be interested in Elaine Thomas's video tutorial which is two parts: