Heat a large saucepan or dutch oven to medium heat. Melt the butter and add the onions and a pinch of salt and sauté until translucent but not browned, about 3-4 minutes.
Next, add garlic, canned tomatoes, and stock and bring to a boil and let simmer for an additional 5 minutes or so to let the flavors come out. Then, using an immersion blender, puree the soup until velvety and smooth.
Finally, add in miso paste and heavy whipping cream and stir until completely dissolved. Taste and season with salt and pepper if needed.
Notes
This is a great make ahead recipe to put on the back burner while preparing other dishes.