Pour Dr Pepper into a medium saucepan and bring to a boil. Turn the heat down to medium-low and simmer (uncovered) until reduced to a syrupy consistency, about 20-30 minutes, stirring occasionally.

In a small glass or bowl, combine the cornstarch and water. Quickly pour into the Dr Pepper and stir constantly until thickened, about 2-3 minutes. Remove from heat.

Preheat the oven to 450 degrees F.

Season salmon with salt and pepper. Place salmon, skin side down, on a non-stick baking sheet or in a non-stick pan with an oven-proof handle. Bake, basting with Dr Pepper glaze 2 or 3 times during baking, until salmon is cooked through, about 12 to 15 minutes. Cook until the fish flakes easily with a fork.

Preheat grill for medium-high heat.

Season salmon with salt and pepper.

Lightly oil grill grate. Place salmon on the preheated grill, fish side down/skin side up. Grill for 3-4 minutes per inch of thickness on each side with the lid closed, or until the fish releases easily from the grate. Once you have flipped the fish, baste salmon 2 or 3 times during cooking with Dr Pepper Glaze. Cook until the fish flakes easily with a fork.