In a medium saucepan, combine the brown sugar, granulated sugar, cream, milk, butter, and salt. Cook over medium heat, stirring constantly, to 230°F Lower heat slightly if the mixture threatens to boil over.
Add the pecans and continue cooking, stirring constantly, to 236°F The mixture should form a soft ball when a little is dropped in cold water. Remove from the heat and add vanilla; let stand for about 5 minutes. Stir with a wooden spoon until the mixture is thickened and slightly creamy, about 1 to 1 1/2 minutes.
Using a tablespoon or small cookie scoop, spoon the pralines onto a sheet of parchment paper or waxed paper. If the mixture becomes grainy, heat and stir over medium heat for a few seconds, or until it can be easily scooped and dropped.
Optional Toasted Pecans:
Heat oven to 350°. Spread chopped pecans out on a large baking sheet. Bake for about 5 minutes, or until the chopped pecans are lightly browned and aromatic. This can also be achieved by microwaving pecans on a microwave-safe plate in 30 second increments.