Place the butter and sugars in a stand mixer fitted with a paddle attachment. Beat on medium-high speed until light and fluffy, 3 to 4 minutes.
Add eggs one at a time, mix until smooth on low speed. Beat in vanilla and peppermint extract.
Slowly mix in baking powder, baking soda, salt and flour, being careful not to over mix. I usually stop when I still have some flour remnants around the bowl.
Chop up the chocolate bar into chunks, trying to keep some large and some small for different variants of melty chocolate puddles. Fold the chocolate chunks, chocolate chips and crushed up candy cane pieces.
Scoop the dough into large balls, I like to use the ¼ cup cookie or ice cream scoop. At this point you can either have the patience to chill the dough knowing the results will be better, or bake your cookies because you just can't seem to resist. I like to scoop out all the balls and lay them out on a parchment lined cookie sheet, and then refrigerate for at least 2 hours, I like to try and do 24 hours.
When ready to bake, turn the oven on to 365 F, and line 2 cookie sheets with parchment paper. Place 6 chilled cookie dough balls on the cookie sheet, sprinkling with the flaked sea salt. Some people salt their cookies after they bake them, but I like to do both. This gives the salt that falls off the tops an opportunity to bake underneath the cookie and give even that much more flavor.
Bake the cookies for 12-14 minutes. You're looking for a nice golden brown outside, with a slightly glossy texture to the inside. If your cookies don't come out in a perfect circle, I like to take a spatula and circle the rim of the cookie to bring in any spots that have spread a little too far.