Preheat oven to 350 degrees. Line a 9 by 12-inch baking pan with parchment paper.
Combine the butter and Sunbutter together in a large heat-safe mixing bowl. Melt in the microwave or over a pot of simmering water. Stir until smooth. Add the brown sugar, eggs, and vanilla and mix well. Combine the flour and baking powder, mixing well. Add to the Sunbutter mixture and stir well to combine. Place the batter in the freezer to cool for about 5 minutes or let cool at room temperature. Stir in the chocolate. Spread the batter into the prepared pan. Sprinkle lightly with sea salt. Bake for 20-25 minutes or until golden and set. Let cool.
Cut into bars or squares and serve. Can be stored covered in the refrigerator for up to 5 days.