In a large bowl, beat the softened butter until smooth and creamy.

Add the granulated sugar and brown sugar. Mix until light and fluffy.

Beat in the eggs and vanilla extract until fully combined and smooth.

Add the flour to the bowl. Sprinkle the baking soda, salt, and cream of tartar over the flour. Mix gently until just combined—do not overmix.

Scoop the dough into balls about 1½–2 inches wide.

In a separate bowl, mix the sugar and cinnamon. Roll each dough ball in the mixture to coat.

Place dough balls on the prepared baking sheets, leaving about 2 inches between each.

Bake for 9–11 minutes, until the edges are set but the centers are still soft.

Remove from the oven and let the cookies rest on the pan for 3–5 minutes, then transfer to a cooling rack.

While still warm, roll each cookie once more in the cinnamon sugar for extra flavor.