For the blondies: Preheat the oven to 350 degrees F. Grease an 8-inch square pan with cooking spray and line with parchment paper.
In a large bowl, whisk together the flour, brown sugar, salt and baking powder. In a separate bowl, whisk together the olive oil, vanilla and eggs. Stir the wet ingredients into the dry ingredients and pour the mixture into the pan, spreading it out evenly.
Bake until the center is set; begin checking for doneness at 35 minutes. Let cool in the pan on a rack for 10 minutes, then remove to the rack and cool completely.
For the frosting: Use an electric mixer to beat together the confectioners' sugar, butter, cocoa powder, heavy cream, vanilla and salt.
Spread the frosting on the blondies, top with sprinkles (if desired) and cut into squares. Store in an airtight container in the fridge for up to a week.