Heat your cast iron pan and 2 tablespoon olive oil to medium-high heat. Then add minced garlic and diced shallots to the pan. Sautee for 5 minutes.
Once the garlic and shallots have sauteed, add your lemon juice, chicken broth, salt and pepper. Let this simmer for another 5 minutes.
Once the liquid is at a rolling simmer, add the arrowroot powder. Be sure to whisk this thoroughly right away until there are no clumps left. Simmer for 5 minutes or until the liquid begins to thicken.
In the mean time, pat your shrimp dry and season with salt and pepper. When the liquid starts to thicken you can add them to the pan. Cooking for 4 minutes on one side and 2 minutes on the other.
When you flip the shrimp add your parsley and capers and let the liquid continue to thicken. If it does not thicken, you can slowly add a slurry of a small amount of arrowroot powder and a tablespoon of water. Don't add this too quickly though, it takes a few minutes for it to thicken.
When it is ready, garnish with extra parsley, serve, and enjoy!