1. Melt the butter in a large saucepan over medium-high heat. Add parsnip and next 8 ingredients (through garlic); sauté 8 minutes. Add stock, 2 cups water, and vinegar; bring to a boil. Cover, reduce heat, and simmer for 30 minutes or until parsnips are tender. Remove from heat; uncover. Let mixture stand 10 minutes.
2. Place half of the parsnip mixture in a blender. Remove center piece of blender lid (to allow steam to escape); secure blender lid on blender. Place a clean towel over opening in blender lid (to avoid splatters). Blend until smooth. Strain the mixture through a sieve into a bowl, and discard solids. Pour into a large bowl. Repeat procedure with remaining parsnip mixture. Top each serving with 1 tablespoon yogurt. Sprinkle evenly with parsley and bacon.