Whisk the flour, baking soda, cream of tartar, and salt together in a medium bowl. Set aside.

In a large bowl using a hand mixer or a stand mixer fitted with paddle attachment, beat the butter, brown sugar, and granulated sugar together until completely creamed and smooth, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Add the egg and beat until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl as needed. Add the peanut butter and vanilla extract and beat until combined.

Add the flour mixture to the wet ingredients and beat on low speed until combined. Add the chopped peanuts and beat until just incorporated. The dough will be very creamy and soft. Cover and chill the cookie dough in the refrigerator for at least 3 hours, and up to 3–4 days.

Preheat oven to 350°F (177°C). Line large baking sheets with parchment paper or silicone baking mats. Set aside.

Place remaining 1/3 cup (70g) of sugar into a bowl, and mix in the cinnamon. Roll chilled cookie dough into balls, about 1 heaping Tablespoon (25g) of dough each. Roll each ball generously in the cinnamon sugar and arrange on baking sheets about 3 inches apart.

Bake for 11–12 minutes or until the edges appear set and are very lightly browned. The centers will still look very soft.

Remove from the oven. Cool cookies on the baking sheets for 10 minutes before transferring to a cooling rack to cool completely. Cookies puff up in the oven, but slightly deflate as they cool.

Cover and store leftover cookies at room temperature for up to 1 week. Their flavor is even better on day 2!