I made this LEGO Birthday Cake for my son's 8th birthday party. I began with one 9 x 13 cake and three mini-loaf size cakes. The 9 x 13 cake I cut into 3 equal pieces and stacked to make it look like a tall stack of 3 LEGO bricks on top of each other. I froze the 3 sections of cake to make it easier to frost them. After freezing for several hours, I frosted the cakes with buttercream frosting and stacked them on top of one another. Over the top of all this, I laid the piece of white fondant icing that I had rolled out to the size of my cake.
After smoothing the fondant on this white cake, I gently scored a line all around the cake on every side at 2 levels (to make it look like there were 3 bricks stacked on top on one another.) Then I cut out six circles of fondant icing to place on top of the tall cake to make the little knobs of the LEGO brick. I followed a similar pattern for the remaining smaller bricks, using two mini-loaf size cakes for 6-piece bricks and one mini-loaf cake I cut in half to make (2) small 4-piece bricks.
I bought and used Wilton fondant that was already colored in primary colors (red, yellow, blue and green) for the smaller bricks and I used Duff Fondant (from Michael's) for the large white brick. The Duff fondant was both better tasting AND easier to use than the Wilton fondant (IMO.)
I tried several different things to make the knobs on the smaller bricks including marshmallows (cut in half) and crispy rice treats cut into the shape of a small cylinder- which was the easier of these two techniques (IMO.) The fondant did not want to stick to the soft marshmallows (even when coated in buttercream!) I wish I had made them all with "flat" knobs like the white cake (which I did by using a circle fondant cutter to cut out uniform circles)- but that was my last technique to try making them- and by far the easiest!! (Even if they didn't look as "real")
I finished the look of my LEGO cake by displaying it on a green base from my son's LEGO collection (with a cutting board underneath, for support!) This is not my first cake to make for my kids' birthdays, but I am by no means an expert! You can do it too!!