In a large pot or Dutch oven over medium to medium-high heat, melt butter. When it foams, melt miso into butter and whisk to combine. Add the onions, partially cover, and soften a few minutes, then add garlic, corn cobs, stock, water, and bay leaves. Raise heat to bring to boil, then reduce heat to low, rolling boil and cook 30 minutes. Remove the bay leaves and cobs, then puree with immersion blender. For a smoother soup, transfer to high power blender and process on soup setting.
Serve soup garnished with sweet chili sauce or hot honey, sliced mild or hot fresh chili peppers and scallions.