- First, prepare your ingredients. We chopped (and promptly refrigerated!) the tuna, and thinly sliced the cucumbers and mango. We chopped the avocado and tossed it with a bit of rice vinegar to prevent oxidization.
- Decide what you'll be using as your cake mold, and line it well with plastic wrap. Be sure to leave the ends of each piece of plastic hanging over the edges. Not only will you need to fold these over the cake when pressing it, they will help you unmold the cake!
(For reference, we used a 4" springform cheesecake pan, and it made probably 3 servings worth of sushi.)
- Have a bit of a design in mind before you start placing your items. For our part, we wanted the cucumbers to look like "swags" on a birthday cake. Because this would be an outermost part of the design, we placed them first, in a ring around the bottom of the pan (which becomes the top when the cake is inverted!). You could also place a design of vegetables, fruit, sesame seeds, or fish on the bottom of the pan.. creating a build-in design when the cake is inverted. You know, like a sushi upside down cake!
Once the cucumber border was in place, we pressed a layer of plain white sushi rice into the bottom of the pan, to be a clear, perfect cake "top". This also helped hold the cucumbers in place.
To make the "sprinkled" side of the cake, I mixed a generous amount of masago in with some white sushi rice, and firmly pressed it evenly along the side of the pan.
Once the sides were pressed in, we started layering the ingredients. The first layer was a round I cut from a nori sheet, followed by mango slices.
Anyway, we continued layering ingredients until the pan was almost full, pressing down firmly and evenly whenever we could. We ended with a final layer of rice, to make it easier to handle.
Once the pan is full, fold the ends of the plastic wrap in and over the cake, and press down FIRMLY and evenly to compact the cake. We happened to have a small plate that fit perfectly inside the springform pan, so we used that to press it all down.
If you're going to chill it, chill it now.
To serve, peel back all of the plastic wrap and carefully invert the cake onto a serving plate.
Once the cake is inverted, feel free to decorate it further. We decided to mix up some wasabi to pipe "Happy Birthday" on top, and a little bead border along the bottom edge. I just used a regular pastry bag... and if we'd had more wasabi powder on hand, I would have made more wasabi, thicker, and piped a rose from it! (If you do this, freeze the rose for a few minutes after piping to make it easier to transfer to the cake)
To serve, slice with a VERY clean, very sharp knife - I rinse with cold water between each slice. Serve with soy sauce, and eat with a fork and knife.