In a large pot add 12 cups of water and bring to a boil. Shuck the corn, cut the kernels off and add the cobs and husks to the boiling water. Season with salt and boil the cobs for 45 minutes. Strain and reserve the liquid.
In the same large pot add the butter and vegetable oil. Stir in the onions and red bell pepper and cook for 5 to 7 minutes.
Stir in the corn cob broth, bring to a boil and turn down to a simmer. Add half the corn, season with salt and pepper and cook an additional 3 to 5 minutes.
Puree the soup with an immersion blender and then stir in the rest of the corn and tomatoes.
Turn off heat and add the basil. Serve soup topped with pepitas.