Step 1In a large saucepan over medium heat, melt 2 1/2 tablespoons butter. Add the onions and cook until softened and translucent, about 5 minutes, stirring occasionally.
Step 2Stir in 1 tablespoon Cajun spice, corn and chicken stock and bring to a simmer. Cook until the corn is cooked through, about 20 minutes.
Step 3While the soup is cooking, saute the shrimp. Season the shrimp with the remaining Cajun spice. Heat a large saute pan over high heat, melt the remaining butter and quickly saute the shrimp until warmed through, about 2 minutes. Remove from heat and move the shrimp to a bowl. Set aside in a warm place.
Step 4Stir the heavy cream into the soup and heat to a gentle simmer. Cook an additional 10 to 15 minutes to thicken the soup slightly.
Step 5Remove from heat and puree the soup until smooth. Adjust the seasoning as needed and stir in additional cream if desired. Stir in the cooked shrimp.
Step 6Serve the soup garnished with a sprinkling of chopped parsley.