Preheat the oven to 350 degrees.

In a medium bowl, whisk together the flour, baking powder and salt. Set aside.

On medium low speed, beat the butter and sugar for about three minutes, until it is light and fluffy. Then add the vanilla, and one egg at a time, combining for about thirty seconds after each addition.

Gradually add the flour mixture until it is well combined, scraping down the sides of the mixing bowl as necessary.

Press the cookie dough into the bottom of a 9x13 inch pan and bake for about 30 minutes. Let it cool on the counter for about 10 minutes, and then put it in the refrigerator for a half hour.

Once the cookie bar layer is completely cooled, melt the chocolate chips and butter together in the microwave in 30 second intervals, stirring in between until fully combined. Pour over the sugar cookie bars. Sprinkle with the peppermint chips. Allow the chocolate to set completely before cutting.