Preheat the oven to 350°F. Grease a 9X13 inch glass or ceramic baking pan.
In a bowl, stir together the butter and brown sugar. Add the egg and vanilla. Whisk until smooth.
In a small bowl, mix together the flour, baking powder and 1/2 tsp salt. Add to the butter and sugar mixture.
Fold in the toffee pieces and chocolate chips but reserve 1/2 cup of chocolate chips for later.
Pour the batter into the pan and spread evenly. Bake for 25 to 30 minutes or until top is golden and a toothpick stuck in the center comes out clean.
Melt the remaining 1/2 cup of chocolate chips in a double boiler or microwave oven. Drizzle the melted chocolate over the baked cookie bars. Sprinkle with sea salt. Cool for 20 minutes before cutting into 32 squares.