Preheat oven to 375°F (190°C). Line baking sheets with parchment paper.
Whisk dry ingredients: In a medium bowl, combine flour, cream of tartar, baking soda, and salt.
Cream butter & sugar:In a large bowl, beat the butter and sugar together until light and fluffy (about 2–3 minutes).Add eggs and vanilla and mix until combined.
Add dry ingredients:Gradually mix in the dry ingredients until a dough forms.
Fold in peaches:Gently stir in diced peaches. (Pat peaches dry with a paper towel first if extra juicy.)
Make cinnamon sugar:In a small bowl, mix cinnamon and sugar.
Shape and roll:Scoop tablespoon-sized balls of dough and roll them in the cinnamon sugar.
Bake:Place cookies 2 inches apart on baking sheets. Bake for 10–12 minutes, or until edges are set and tops are slightly crackled.
Cool:Let cookies cool on the sheet for 5 minutes, then transfer to a wire rack.
Notes
Storage Tips:Store in an airtight container at room temperature for up to 4 days.Freeze baked cookies for up to 2 months; thaw at room temp before serving. Pro Tips:Use ripe but firm peaches to avoid soggy dough. Let cookie dough chill 30 minutes if it's too soft to scoop. If you use gluten free flour chill dough before scooping and also when formed into balls. GF flour tends to spread during baking. Slightly underbake for the softest, chewiest texture