Step 1Trim the artichokes, removing the leaves and trimming any outer hard green portion left on the bottoms. Cut the heart in half and discard the fuzzy choke. Bring a small pan of water to boil. Add the lemon juice and 1 teaspoon of salt. Then add the artichoke heart halves, cooking until just tender, 4 to 5 minutes. Drain. When cool enough to handle, dice the artichoke. You'll have about two-thirds cup diced artichokes.
Step 2In a small bowl, mix the sugar, soy sauce, rice wine and cornstarch. Stir in the shrimp. Marinate for 15 minutes.
Step 3If using the rice sticks, place 2 to 3 cups of oil in a small deep-sided saucepan. Heat the oil to 375 degrees. Add the rice sticks and remove when they puff and float to the surface, a few seconds. Transfer to a paper-towel-lined baking sheet or plate. Let the noodles cool. Break into small pieces and put in a small serving bowl. Set aside.
Step 4Heat 1 tablespoon of oil in a nonstick skillet. Add the garlic and cook until golden, about 1 minute. Add the shrimp and stir-fry. When the shrimp is almost cooked through, add the remaining tablespoon of oil, diced artichoke, lemongrass, green onions, vinegar and cilantro. Heat through. Season with salt and white pepper.
Step 5Transfer the filling to a bowl and serve with radicchio leaves and, if using, puffed rice sticks.