Preheat oven to 350° F and line 2 baking sheets with parchment paper.
Stir the flour, cream of tartar, baking soda, and salt together in a bowl.
In a large bowl, cream the butter and sugar until light and fluffy. Add the eggs one at a time and beat until thoroughly combined.
Add the flour mixture all at once and stir until well mixed, with no dry spots remaining. In a small bowl, combine the sugar and cinnamon for rolling. Spoon the Nutella in a pastry bag fitted with a small round tip (or a plastic zip-top bag: Fill with Nutella, then cut the corner).
Scoop the cookie dough into rounded tablespoon-sized balls, about 1 1/2 inches big. Flatten the balls, making a small well to fill with the Nutella. Pipe a scant teaspoon of Nutella into each well then use your fingers to press the cookie dough around the Nutella, sealing it in the ball. Alternately, carefully spoon the Nutella into the wells. Roll the dough balls in the cinnamon sugar, then place them on one of the prepared baking sheets. Freeze the dough balls for 15 minutes before baking.
To bake: Arrange the cookies on the baking sheets, about 3 inches apart. Bake the cookies for 11 to 15 minutes, until puffy and barely golden around the edges, rotating the pans from top to bottom and front to back halfway through the baking time.
Yossy Arefi is a photographer and stylist with a passion for food. During her stint working in restaurant kitchens, Yossy started the blog Apt. 2B Baking Co. where, with her trusty Pentax film camera, she photographs and writes about seasonal desserts and preserves. She currently lives in Brooklyn but will always love her native city of Seattle. Follow her work at apt2bbakingco.blogspot.com & yossyarefi.com.