In a large Dutch oven, over medium heat, melt the butter. Add the onion and sauté, stirring occasionally until translucent, about 2-3 minutes. Add the garlic and sauté until fragrant, about 1 more minute. Add the carrots, potato, coriander, and sauté for 2-3 minutes, coating the vegetables with the butter. Add the stock, sugar, and salt, and raise the heat to medium-high. Bring to a simmer, reduce the heat to medium-low, cover, and continue to cook until the vegetables are soft when pierced with the tip of a knife, about 20-30 minutes. Remove from the heat.