Preheat oven to 350°F. Line a metal 9x13-inch pan with foil and spray with nonstick cooking spray.
Cream butter and brown sugar in a large bowl until fluffy, 1-2 minutes. Add eggs, baking powder, vanilla, and salt and mix until smooth, then slowly mix in flour. Stir in candy.
Press batter into prepared pan and bake until it loses its glossy sheen and is very light golden around the edges, about 20-25 minutes. Cool completely before frosting. Slice into bars.
Store in an airtight container for up to 3 days or freeze for up to 3 months.
Notes
These blondies are best enjoyed fresh but can also be frozen for later.