Preheat oven to 350F. Spray an 8" square baking pan with nonstick cooking spray or grease the pan with butter.
Beat brown sugar, butter, and vanilla in a bowl with an electric mixer at medium speed until smooth and creamy. Add the egg; beat until fluffy. Add the flour, pumpkin, pumpkin pie spice, baking powder, and salt; beat at low speed just until blended. Stir in toffee bits. Spread batter evenly in the prepared pan.
Bake 40 to 45 minutes or until a toothpick inserted in the center comes out clean. Cool completely in the pan set upon a wire rack.
Prepare the frosting and spread over the cooled brownies.
White Chocolate Cream Cheese Frosting:
- Heat 2 tbsp whipping cream in a small saucepan over medium heat until almost boiling - remove from heat.
- Add 4 oz chopped white chocolate; stir until completely melted. Cool slightly.
- Beat 6 oz softened cream cheese and 1/3 cup powdered sugar (sifted) in a large bowl with an electric mixer at medium speed for about 1 minute or until fluffy.
- Add white chocolate mixture; beat until smooth.
* A substitute for pumpkin pie spice:
1 tsp ground cinnamon
1/2 tsp ground ginger
1/4 tsp ground allspice
1/4 tsp ground nutmeg