Preheat oven to 350F (175C) and line baking sheets with parchment paper. Set aside.

In a large mixing bowl, use an electric mixer to cream butter and sugar until well combined.

Add egg, egg yolk, and vanilla and stir until well combined.

In a separate, medium-sized bowl, whisk together flour, cream of tartar, baking soda, and salt.

Gradually add dry ingredients to wet, stirring until completely combined. Prepare the cinnamon ripple.

In a separate, medium-sized bowl, prepare the ripple by whisking together sugar, cinnamon, and salt until well combined. Add butter and toss together until mixture resembles a paste.

Gently fold the paste/ripple into cookie dough using a spatula, careful not to mix too much so you still have a distinct ripple.

Scoop dough by level 1 ? Tablespoon-sized scoop and (optional) roll gently between your palms to create a smooth ball.

Place cookie balls on prepared cookie sheet, spacing at least 2? apart and transfer to center rack of preheated oven to bake for 10-11 minutes.

Allow cookies to cool completely on baking sheet before enjoying.