Preheat oven to 350 °F (175 °C) and line a baking sheet with a piece of parchment paper.
Using an electric hand mixer or a stand mixer with the paddle attachment, cream the butter and sugar until light and fluffy.
Beat in the extract, lemon zest if using, and egg just until combined. It'll not be smooth but rather lumpy.
Sprinkle the baking soda, baking powder, salt and cream on tartar on top and stir in until combined.
Add the flour and beat on low until a dough forms.
Place in the fridge for 20 minutes.
Take the dough out and roll into 2-tablespoon balls (each about 40 grams), and place 3" apart on the prepared baking sheet. Gently flatten them a bit with the palm of your hand.
Bake for 10 minutes or until the tops no longer appear wet and are a bit puffy and crinkly on top. The cookie bottoms will be a light golden brown color, but the tops and edges of the cookies won't be. If they've browned, they'll be dry and cakey.
Let cool for 2 minutes on the baking sheet and then transfer to a wire rack to cool completely.