Preheat your oven to 400 degrees. Trim the husks on the top of the corn cobs, and place in the oven for 30 minutes. Remove from oven and set aside to cool.
Once cool, slice the corn off the cob into a large bowl. Add the sour cream, cotija cheese, chili powder, garlic, and cilantro in a large bowl. Stir and set aside.
Cook the shells according to package directions, drain and set aside.
In a sauce pan over medium heat, add the olive oil and butter. Whisk in the flour and cook for 2 minutes until beginning to brown. Whisk in the milk and cook for 3-5 minutes, until the milk has thickened. Add the cheddar cheese, salt, pepper and garlic.
Once the cheese is incorporated, add the shells and stir to combine. Remove from heat.
To serve, plate the pasta and top with a generous spoonful of the street corn topping.