Preheat oven to 375°. Place the rinsed sushi rice in a small saucepan. Add water and place over med heat. As soon as bubbles start to form on the edges, stir to release anything sticking and cover with a lid. Reduce heat to low. Cook for 15 minutes and then turn off heat (don't open the lid). Allow to steam for another 10 minutes. Remove lid, fluff with fork. Add rice vinegar, sugar, and sesame seeds or furikake and fluff again. Set aside and allow to rest until just warm.
Preparing the Roll
While rice is cooking, prepare the Brussel sprouts and charred lemon. Toss quartered Brussel sprouts and sliced lemon with olive oil in a small roasting pan. Season with salt and pepper. Roast for 20-25 minutes until sprouts are tender and lemon is caramelized. Remove from oven and allow to cool until safe to handle.
Once rice is done, place one nori sheet (bumpy side up) on a piece of parchment paper. Using a fork and wet fingers, press cooked sushi rice onto the mat firmly leaving 1-2 inches of nori uncovered. Carefully flip the nori over so that the rice is facing down.
Arrange your Brussel sprouts and lemon slices on the edge of the nori that does not have rice under it. Top with some prosciutto. You are going to roll that uncovered nori around the filling to get it started. Don't over do the filling. 6 small Brussel quarters and half of a strip of prosciutto should be enough.
Pick up the edge of your rolling mat and start to flip the exposed piece of nori over the filling ingredients. You essentially want to tuck that piece around and under to get your roll sealed. Lift the parchment and flip it over the roll. Use it as a guide to begin rolling while also pulling it back towards you, and use your fingers to pinch the roll firmly as you go. You want to get things tight on that first turn and then continue rolling about a half turn at a time, pulling the mat free as you continue to roll forward and continuing to pinch along the length of the roll as you go. Unroll the parchment and you should have a beautiful sushi roll!
The hardest part IMO is cutting. Move the roll to a cutting board and lay a piece of parchment over the top. Use your fingers to hold the parchment and roll firmly while sliced with a serrated knife, gently sawing back and forth as you go. Carefully remove the parchment. Stand back to admire what you've created, then go ahead and make your second roll. Serve immediately or keep wrapped in plastic and refrigerated until ready to serve.
Serve 1 roll per person with soy sauce for dipping and wasabi paste on the side (optional).