How to Make It
Remove leaves from cilantro bunch, and set leaves aside for garnish (about 1/4 cup). Combine stock, water, garlic cloves, ginger, lemongrass, and remaining cilantro stems in a medium saucepan over medium-high. Bring to a boil, and let simmer to infuse flavors, 10 minutes.
Add chicken to pan; reduce heat to medium-low, and keep cooking liquid between 160°F and 180°F. Cook chicken until a thermometer inserted in thickest portion registers 160°F, 25 to 30 minutes. Remove chicken from cooking liquid, and let cool 15 minutes. Shred chicken. Pour cooking liquid through a fine wire-mesh strainer into a bowl; discard solids.
Return cooking liquid to saucepan over high; bring to a boil. Prepare rice noodles in cooking liquid according to package directions. Reserve 1 cup of the cooking liquid. Drain noodles and rinse with cold water; drain.
Toss together cabbage, 1 teaspoon of the lime juice, 1/2 teaspoon of the sugar, and 1/4 teaspoon of the salt in a large bowl until combined. Let stand at room temperature 15 minutes.
Heat oil in a medium saucepan over medium-high. Add curry paste; cook, stirring often, until fragrant, 1 minute. Stir in coconut milk and reserved cooking liquid, stirring well to combine; bring to a boil. Reduce heat to low; simmer until reduced to 2 1/2 cups, about 2 minutes. Stir in remaining 5 teaspoons lime juice, 1/2 teaspoon sugar, and 3/4 teaspoon salt.
Arrange noodles and chicken in each of 4 shallow bowls. Ladle broth over each serving; top with cabbage mixture. Serve with lime wedges, and sprinkle with cilantro leaves.