Directions:

Preheat oven to 400°F (205°C).

Sift flour, cream of tartar, baking soda, and salt in a mixing bowl and set aside.

Cream together the butter and sugar using a hand mixer, about 3 minutes. Add egg and egg whites, one at a time, and continue to mix. Scrape down the sides of the bowl. Stir the flour mixture into the butter mixture until fully incorporated.

Form dough into a disc, cover with plastic wrap and refrigerate for an hour.

In a small bowl, stir together the sugar and cinnamon.

Roll 1 1/2 tablespoons (25 mL) of the chilled dough into a ball and roll around the cinnamon sugar mixture until completely coated and place onto a baking sheet covered with parchment. Repeat until all the dough has been used; you'll need two baking sheets.

Bake the snickerdoodles for 10 to 12 minutes or until the edges just start to brown. Transfer cookies onto a cooling rack and allow to cool. Serve.