1 package nori sheets (10 sheets per package), or more as needed
1 batch prepared sushi rice
1/4 cup seasoned rice vinegar, in a small bowl
Wasabi sauce, wasabi paste, or other condiment of your choice (hoisin, horseradish, hot mustard, etc.)
Assorted cold vegetables, cut into long, thin strips: red pepper, yellow pepper, carrots, cucumber, steamed asparagus, avocado, etc.
Place the sushi mat on your work surface. Hold one nori sheet with a pair of long tongs, and toast it briefly over the gas burner on your stove (you can skip this step if you're starting with roasted nori). Place the nori sheet shiny side down on the sushi mat, with the lines in the nori aligned with the bamboo slats of the mat.
Dip your fingertips in the bowl of rice vinegar, and take a blob (3-4 tablespoons) of sushi rice. Place the rice in the lower end of the nori (closest to you), and with your fingers, spread it evenly over the lower half of the nori, leaving a half-inch margin on the long side closest to you, and on each end. (This is just like making strudel or a buche de noel.)
Spread a small strip of wasabi sauce (or other condiment) down the middle of the rice. Then lay several strips of vegetables on top of the wasabi sauce.
Now it's time to roll! Starting with the end closest to you, lift the edge of the bamboo mat. Using your fingers to keep the rice and vegetables in place, roll the mat over until the nori meets itself. Lift the top edge of the mat, and press the roll to keep its shape. Using the mat to help you, slowly begin to roll the nori away from you, tucking the roll into shape and pulling the mat out and back towards you at the same time. The moisture in the rice will help the roll stick together. Roll and tuck until you get to the end; if necessary, dab the end with a bit of water to make sure it stays closed.
With the seam side down, take a very sharp, clean knife and slice the nori roll in half. (Wipe the knife clean between each cut.) Then, slice each half into 3 pieces, making six pieces in all. Serve with pickled ginger and your choice of dipping sauce.