Melt the butter in a large soup pot over medium high heat. Add chopped onion and minced garlic and cook until soft, stirring frequently so they don't burn, about 5 minutes.
Add vegetable broth, peas, salt and pepper. Bring to a boil and then cover and simmer until the peas are soft, about 15-20 minutes.
Using a immersion blender, blend the soup until creamy. Alternatively you could use a blender. If using a blender, carefully put soup in blender in batches, and pulse until creamy, being careful as the soup is very hot. Put soup back in pot if using a blender.
Add in heavy cream and stir to thicken up. Season with salt and pepper to taste and serve. Optional - add some fresh parsley or mint on top before serving.
Notes
Don't have whipping cream? You can substitute plain yogurt or sour cream instead.