Rinse the rice in cold water 4 or 5 times, swishing with your hand and pouring off the milky water, until it runs mostly clear.

Combine the rice and 1 cup plus 2 tablespoons water in a small saucepan and let it soak 15 minutes. Bring to a boil, cover, reduce to the lowest heat and cook 15 minutes.

Remove from the heat and let it stand covered for 10 more minutes without lifting the lid.

Stir the rice vinegar, sugar and 1 teaspoon salt together until dissolved. Spread the hot rice in a wide bowl, pour the seasoning over and fold it in with a slicing motion. Cool uncovered about 20 minutes, to body temperature.

Heat the oven to 425 degrees F. Toss the sweet potato batons with the oil and ¼ teaspoon salt and spread them on a sheet pan with space between them.

Roast 22 to 25 minutes, turning once, until the edges are dark and sticky and the centers are soft. Cool at least 10 minutes.

Wrap a bamboo mat in plastic wrap and lay one nori sheet on it, shiny side down. Keep a bowl of water nearby for your hands.

With wet fingertips, spread about ¾ cup of rice evenly over the nori, leaving a bare 1 inch border along the far edge.

Lay 2 or 3 sweet potato batons end to end about a third of the way up from the near edge, with a single row of avocado slices alongside.

Lift the near edge of the mat, tuck it over the filling and pull back gently to tighten, then roll forward. Dab the bare nori with wet fingers to seal and rest the roll seam side down 2 minutes.

Cut each roll into 8 pieces with a very sharp knife, wiping the blade with a damp cloth between cuts. Sprinkle with sesame seeds.

Stir the mayonnaise and sriracha together and drizzle over the rolls, or serve soy sauce alongside.