Preheat oven to 450° F.
Make guacamole: Combine all ingredients, mashing avocado with the back of a fork until it's a chunky consistency. Set aside.
Line a baking sheet with parchment paper or aluminum foil. Put corn kernels on baking sheet and toss with oil, 1/4 tsp salt and black pepper to taste.
Spread corn out evenly on baking sheet and roast for 20 minutes, until corn turns a golden brown. The corn will caramelize and get a little crunchy.
Remove corn from oven and set aside.
To prepare the corn for the soup, put kernels (fresh or frozen and defrosted) in a blender. Combine oil and garlic in a soup pot over medium heat.
Add onion and jalapeño. Season with salt and pepper and sauté until vegetables are soft and translucent, for about 6 minutes.
Transfer vegetables to blender and puree until smooth. (You may need to pulse or stir corn mixture in order to achieve a smooth consistency, but do not add any more liquid.)
Pour corn puree into soup pot and place over medium heat. Stir constantly for a few minutes, until soup begins to thicken.
Slowly whisk or stir in chicken broth. Bring to a boil, decrease heat to a simmer, cover, and cook for 15 minutes.
Ladle soup into bowls, top with roasted corn guacamole. Serve immediately.