Preheat oven to 350ºF. Line a 9″ square pan with aluminum foil and grease foil with nonstick spray.
In a large bowl, whisk together the brown sugar and melted butter until well-combined. Add the egg and vanilla extract and beat in until the mixture is smooth and slightly lighter in color.
Add the flour, baking powder, and salt and fold in until mostly incorporated. Fold in the caramel candy just until all ingredients are evenly combined.
Transfer batter to prepared pan in a flat, even layer, smoothing the top out with a spatula. Bake in preheated oven for 25-30 minutes, until a toothpick inserted into the center of the blondies comes out clean. Cool completely before adding ganache.
Combine the chocolate and 1 ounce (2 tablespoons) butter in a large, microwave-safe bowl. Microwave for 30-second increments, stirring in between, until smoothly melted. Add the remaining 1/2 ounce (1 tablespoon) butter and stir in until melted and fully incorporated.
Pour ganache over blondies and spread out in a flat, even layer using an offset spatula. Transfer to refrigerator to cool until firm but not fully set. Score through chocolate (as if you were slicing the blondies to serve) and then return to refrigerator until set. Once set, lift blondies from pan and slice.
Store in an airtight container. Blondies are best served at room temperature.