Heat a stockpot on medium-low, then add the butter and olive oil. Allow the butter to melt then add the onion. Allow it to cook until turning soft and lightly golden in colour, stirring regularly.
Add the leeks and cook until the leeks begin to soften and become slightly sweet.
Stir in the garlic, paprika, and herbs - but reserve half of the fresh marjoram for later. Cook for about 1 minute until fragrant. Then deglaze with the vinegar, scraping up any brown bits stuck to the pan.
Pour in the stock and potatoes, increase the heat to bring the soup to a simmer. Reduce the heat back to low and allow the potatoes to cook, approx 20-25 minutes.
Turn off the heat, remove the bay leaves, add the silken tofu, miso paste and sugar. Blend the soup with a stick blender until silky smooth.
Finish by stirring in the remaining marjoram and taste to adjust seasoning to your preference. Serve with hot buttered sourdough!