Preheat oven to 350F and butter a 9 x 9-inch baking pan. 

Melt butter in a small pot over medium heat. Stir in brown sugar and cook, stirring, until dissolved, about two minutes.

Remove from heat and allow to cool for 10 minutes.

Stir in vanilla and egg, beating well to combine thoroughly.

Whisk together flour, baking powder and salt and add to the butter mixture, stirring until blended.

Add pecans and berries and mix well. 

Spoon batter into the prepared pan and spread evenly with an offset spatula or the back of a spoon. 

Bake for 20 to 25 minutes, until top is golden brown. The centre will sink—don’t worry, this gives the bars their signature chewy texture. Allow to cool to room temperature before cutting into squares.