To make this on the stovetop, simply combine all the ingredients and bring to a boil. Reduce the heat to medium-low and simmer, covered, for about 30 minutes, or until the beets are very tender. Transfer to a blender or food processor and puree until smooth. To make this in a regular slow cooker, combine all the ingredients and cook on high for 2-4 hours, or until the beets are tender. To make this vegan or Whole30-friendly, simply omit the yogurt. You can still garnish with tarragon and a squeeze of lemon. Or substitute coconut yogurt.