In a heavy-bottomed saucepan, combine the brown sugar, granulated sugar, heavy cream, and butter. Cook over medium-high heat and stir occasionally until the caramel reaches the softball stage, 235 to 240 degrees F on a candy thermometer. Alternately, you can drop a small amount of the caramel into a cup of ice water. It should form a ball that is malleable. Once this happens, add the pecans, bourbon, and a pinch of salt to the caramel, and pull the pan off the heat. Stir the pot vigorously with a wooden spoon until it cools slightly and thickens. The pecans will no longer sink in the mixture and it will take on a more matte than glossy finish. Spoon the pralines into small mounds onto a parchment or aluminum foil lined sheet pan and cool completely before serving.