Preheat oven to 350° F. Grease a 9x13-inch baking pan. Set aside.
In a large bowl, beat butter, baking powder, and salt until well blended. Gradually add flour.
Add brown sugar and vanilla extract until blended. Scrape down the sides when needed. Lastly, add the egg and mix well.
Spread mixture into a greased 13x9 baking pan. I found that a regular knife works better than a rubber spatula for spreading.
Bake for 12-15 minutes, until edges are lightly browned and surface is dry.
Immediately after taking the toffee out of the oven, sprinkle the chocolate chips evenly. Let stand for 5 minutes so they melt. Spread chocolate over bars. Sprinkle with nuts and let it stand until chocolate is set.
Cut into squares and then in half into triangles. Store in an air tight container in the fridge.