To make the brown butter, melt butter in a clear heavy bottom pot. Once the butter starts to foam, whisk continuously until brown bits start to form. Remove from heat, pour into clean bowl, skim the foam from the top and cool to room temperature (15 minutes), stir then chill in the fridge an addional 15-20 minutes. The butter should begin to solidify, but shouln't be cold. If its cold, let come to room temperature for 5 minutes.
In a separate bowl, whisk together flour, baking soda and powder, salt and pumpkin spice. Set aside. In a mixing bowl, with paddle attachment, cream together the browned butter, sugar and tahini until light and fluffy (3-4 minutes). Add in eggs and yolk one at a time, beating until each is well incorporated. Add pumpkin and vanilla and beat until well incorporated (about 2-3 minutes).
Add dry ingredients to the wet 1/2 at a time. Mix on lowest setting until JUST combined or by hand. Do not overmix. Gently fold in chocolate chips, chunks or disks. If baking right away, place the cookie dough in the fridge to chill for minimum 30-60 mintues. If freezing see notes. **
Pull dough from the fridge, scoop out using a 2" cookie scoop with trigger release onto aparchment lined baking sheet. Bake at 350F for 14-16 minutes or until cookies are set around the edges. The center may still look slightly underbaked. Pull cookies from the oven, cool on the cookie sheet placed on top of a cooling rack for 3 minutes. Using a spatula, gently removed cookies from the pan, onto a cooling rack and cool an addiotnal 10-15 minutes.