Preheat your to 350°F/177°C. Line cookie sheets with parchment paper.
Place the butter, peanut butter, and sugars in a mixing bowl and using an electric mixer, mix on medium high speed until light and fluffy, about one minute.
Mix in the ground flax seeds, cornstarch, milk, vinegar, and extracts. Continue mixing until light and fluffy again.
Add the flour, baking soda, baking powder, and salt on top. Use a spoon to stir this mixture. Then use your mixer to combine the flour mixture with the butter mixture. Mix to combine.
Add the chocolate chips and sprinkles and mix until they're incorporated throughout the dough.
Use a cookie dough dispenser to make cookie dough balls. Press additional chocolate chips and sprinkles into the top of each cookie. Alternatively, pour sprinkles on a plate and roll cookie dough balls through the sprinkles. Place prepared cookie dough balls 1 ½ inches apart on the prepared cookie sheet.
Bake for 9 to 10 minutes. These cookies are best when they're slightly undercooked so be careful not to over bake. You'll be rewarded with a dense, rich, moist cookie!
Remove the pan from the oven and allow the cookies to cool for up to 2 minutes on the pan before placing on a wire rack to cool completely.
Repeat until all the cookies are baked. Store in an airtight container.