For the horseradish cream: Combine the sour cream, horseradish, salt and some pepper in a bowl. Add the iceberg lettuce and toss to combine.
For the spicy ketchup: Combine the ketchup, Cajun spice and hot sauce in a bowl.
For the burger: Mix the ground beef and salt and pepper blend in a bowl until well mixed. Do not over mix because it will make for a tough burger. Form into 8 patties.
Preheat a flattop to medium-high heat, 300 degrees F, and then place the buttered interior of the buns face down on the flat top, cooking until golden brown. Then remove. Next, add 2 tablespoons grape seed oil to the flat top. Place the burgers on the oiled surface and cook for 2 minutes on each side.
Assemble the tomatoes, onions and pickles on a cutting board. Then spread the spicy ketchup on the bottom bun. Place the first burger on the bun, then layer with tomatoes, onions and pickles. To finish, top with the lettuce mixture, and then stack a second burger on top. Score with a toothpick. Repeat with the remaining ingredients.