Before you get started cooking, prep your veggies: scrub and peel the potatoes, carrots and parsnips and then chop into chunks medium, small, and very small (respectively.) The parsnips take the longest to cook, so in order for all the veggies to be done at once, cut them the smallest, carrots a bit bigger, and potatoes bigger than that. Allow to sit in cold water in a bowl to prevent browning.
In a large deep pan, melt the butter over medium heat and gently cook the onions for 8 minutes, or until softened but not browned. Add in 1 tsp salt, the cumin and the coriander and stir to coat. Cook for an additional minute to allow the spices to bloom.
Add in the drained potatoes, carrots and parsnips and cover, Cook 10 min over medium-low heat, stirring occasionally to prevent any sticking to the bottom of the pan. Meanwhile, heat up your stock to a simmer.
Add in the stock and bring to a boil. Once boiling, reduce the heat, cover and simmer for 20-25 mins or until the vegetables are tender enough to be pierced with a knife.
Remove from heat and allow to cool slightly. Blend smooth in your Vitamix or use your immersion blender. Taste to adjust seasoning (maybe a splash of apple cider vinegar if it needs a bite, but know that the yogurt will add a tang.)
When serving, drop two big spoonfuls of yogurt into each bowl, and garnish with fresh minced herbs or croutons.