Rinse the sushi rice under cold water until the water runs clear. Soak it in water for 30 minutes, then drain.
In a medium saucepan, combine the drained rice and 1 ½ cups of water. Bring to a boil over medium heat, then reduce to low, cover, and simmer for 15 minutes.
Remove from heat and let the rice sit with the lid on for another 10 minutes.
In a small bowl, mix sugar and vanilla extract into the warm rice, fluffing it gently with a fork. Allow to cool slightly.
Place a piece of nori on a bamboo sushi mat, shiny side down. With wet hands, spread a thin layer of sushi rice evenly over the nori, leaving a 1-inch border at the top edge.
In a straight line across the center of the rice, place sliced strawberries and a small dollop of whipped cream.
Starting from the edge of the mat closest to you, carefully roll the nori over the filling, tucking it tightly as you go. Wet the top edge with a bit of water to seal the roll.
Use a sharp knife, lightly moistened, to slice the roll into 6-8 pieces. Repeat with remaining nori and filling.
Drizzle lemon juice over the sushi rolls for a refreshing kick. Dust with powdered sugar before serving.
Notes
Arrange the sushi rolls on a platter, garnish with additional strawberries, and serve with a side of whipped cream for dipping.