To the bowl of a stand mixer fitted with the paddle attachment (or large mixing bowl and electric mixer) combine the egg, peanut butter, butter, sugars, vanilla, and beat on medium-high speed until creamed and well combined, about 4 minutes.
Stop, scrape down the sides of the bowl, and add the flour, cocoa powder, optional but recommended instant espresso granules (doesn’t make the cookies taste like coffee; serves to intensify and bring out the chocolate flavor), baking soda, optional salt, and beat on low speed until just combined, about 1 minute.
Using a large cookie scoop, 1/4-cup measure, or your hands, form approximately 11 equal-sized mounds of dough, roll into balls, and flatten slightly. Even though cookies will spread in the oven, make sure dough mounds are wider than the Turtles; eyeball a Turtle prior to forming dough mounds to make sure.
Place mounds on a large plate or tray, cover with plastic wrap, and refrigerate for at least 2 hours, up to 5 days. Do not bake with unchilled dough because cookies will bake thinner, flatter, and be more prone to spreading.
Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. Place dough mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet) and bake for about 9 to 10 minutes (for super soft cookies, longer for more well-done cookies), or until edges have set and tops are just set; don’t overbake which is easy to do with dark-colored cookies (I baked one batch for 11 minutes and after cooling they were too dry for my liking).
After removing cookies from oven, carefully add 1 Turtle to the center of each cookie, pressing it down slightly so it adheres. As you press down, cookies will likely develop a few cracks around the perimeter, this is okay.
Allow cookies to cool on baking sheet (I don’t use a rack) for about 10 minutes before drizzling with caramel sauce and serving.
Storage: Cookies will keep airtight at room temperature for up to 1 week or in the freezer for up to 6 months. Alternatively, unbaked cookie dough can be stored in an airtight container in the refrigerator for up to 5 days, or in the freezer for up to 4 months, so consider baking only as many cookies as desired and save the remaining dough to be baked in the future when desired.