Place shrimp, shells on, in a large bowl. Add 1 tablespoon olive oil, salt, and pepper and toss.

Heat a cast iron skillet over medium heat until hot; add 1 tablespoon olive oil to the skillet.

Cook shrimp in the skillet, without crowding, for 3 to 4 minutes on each side. You may have to work in batches. Remove shrimp from skillet and allow to cool.

Combine egg, poblano pepper, garlic clove, lime juice, and basil in a food processor and blend until smooth. With processor running, slowly add 1/2 cup grapeseed oil and process until mixture is smooth and thick.