Preheat oven to 350 degrees F (175 degrees C). Spread walnuts onto a baking sheet.
Toast walnuts in the preheated oven until golden brown and fragrant, 8 to 10 minutes. Chop coarsely.
Combine brown sugar and butter in a large bowl; beat with an electric mixer until light and fluffy. Beat in 1/4 cup bourbon, egg, and vanilla extract until batter just combined. Fold in flour, 1/2 cup caramel candies, and salt.
Grease a 9x13-inch baking pan with cooking spray. Spread batter evenly in the pan.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes. Let cool, about 15 minutes.
Heat 1/3 cup caramel candies in a double boiler over medium-high heat until soft and malleable, about 5 minutes. Pour in heavy cream and 1 tablespoon bourbon; stir constantly until combined. Remove from heat and cool slightly, 5 to 10 minutes.
Drizzle or spread caramel sauce over the cooled blondies. Scatter chopped walnuts on top. Sprinkle smoked salt over walnuts.