Preheat the oven to 350°F. Line a 10×15-inch jelly roll pan with parchment paper, leaving some overhang on the sides. Lightly spray the parchment.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter and sugar on medium-high speed for 1 to 2 minutes, or until light and fluffy.
Add the eggs one at a time, mixing until just incorporated after each addition. Mix in the peppermint extract and green food coloring, if using.
In a separate bowl, whisk together the flour, baking powder, baking soda, cream of tartar, and salt.
With the mixer on low, gradually add the dry ingredients. Mix just until combined.
Fold in the chocolate chips and chopped chocolate by hand until evenly distributed.
Press the dough evenly into the prepared pan.
Bake for 17 to 20 minutes, or until the edges look set and the center no longer looks wet or shiny. Be careful not to overbake. The cookies will continue to set as they cool.
Let the cookie cool completely in the pan. Use the parchment overhang to lift it out, then cut into bars.