Spread the pecans on the foil-lined baking sheet and roast until lightly browned and fragrant. Add 2 tablespoon unsalted butter and salt to the hot nuts and stir. Set aside to cool.
In a heavy saucepan over low heat, melt the remaining 2 tablespoons butter. Stir in the granulated and brown sugar, granulated sugar, corn syrup, and heavy cream. Slowly bring to a boil over medium heat. Add the pecans and continue slowly boiling until the temperature reaches 242° F/117° C on the candy thermometer, or almost firm ball stage. If you boil it too fast, the sugar grains don’t fully dissolve and the mixture won’t set properly.
Remove from heat and quickly stir in the vanilla and bourbon using the heat-resistant silicone spatula. Continue stirring vigorously until the candy loses its glossiness, becomes creamy in appearance, and thickens, about 2 to 3 minutes. Don’t stir for too long or it will become grainy.
Very quickly drop the candy mixture by tablespoons onto the baking sheet lined with a silicone mat, about 1 to 2 inches apart. Allow to cool completely. Store at room temperature wrapped in plastic.