First prepare your kohlrabi. Slice off all leaves, and reserve for another recipe like braised greens. Using a sharp paring knife, slice off the top and bottom, and then going around the outside of the bulb, thinly slice off the rest of the outer green or purple peel. The inside is softer and white. Dice into 1/2" pieces and bring a pot of salt water to a boil. If also using potatoes, peel and dice to similar size. When the water is boiling, drop in the kohlrabi. Let it come back to a boil, and then tightly seal (maybe using a round of parchment paper and then the lid) and cook till easily pierced with a knife, appx 15-20 min.
Meanwhile, finely chop the onion and the celery, and mince the garlic. Begin to heat up the stock in a small pot. In a deep sauté pan or dutch oven (large enough to hold all the soup), cook the bacon until nice and brown and crunchy, and the fat is rendered. Remove the bacon to the side. If preparing vegetarian or vegan, use butter or oil. When the kohlrabi is done, reserve a cup or so of the boiling water and drain the kohlrabi chunks.
Turn the heat to medium-low on the bacon fat, and cook the onion in it for 4 minutes until slippery and soft, then add the celery for another 2 minutes, then the garlic for 1 minute more. Add a pinch of salt, and the white wine. Allow the wine to reduce by half, and then pour in the kohlrabi chunks and the pre-heated stock. Cook for 15 minutes, for the flavors to meld together. Remove from heat, and purée with an immersion blender or toss the whole thing into the Vitamix. Taste, and adjust seasoning by adding salt and pepper, and/or thin it out with some of the kohlrabi cooking water.
You can serve warm, but it's better when served as a cold first course. Once it's come down to closer to room temp, cool it off in the fridge for a few hours or overnight. This is a great make-ahead dish.
Serve garnished with minced green onions, chives or celery leaves, a few tablespoons of the heavy cream stirred in (can be omitted or subbed with coconut cream), and some crumbles of the bacon (easily omitted for vegetarian prep.)