Do I really need cream of tartar?
If you want that classic snickerdoodle tang, yes. Cream of tartar is what separates snickerdoodles from cinnamon sugar cookies.
No cream of tartar? For a workable substitute, skip the cream of tartar and baking soda, and use 2 teaspoons baking powder instead. You will still get a great cinnamon sugar cookie, but the flavor will be less tangy and the texture can be a bit more cakey.
Why did my snickerdoodles turn out flat?
Most common culprits: butter that is too warm or shiny/oily, not enough flour (or flour packed down inconsistently), baking soda or baking powder that is old, or an oven that runs hot. Use butter that is soft but still cool to the touch and not glossy, and consider checking your oven temp with a thermometer.
How do I keep them soft?
Do not overbake. Pull them when the edges look set but the centers still look a little puffy and pale. They finish cooking on the hot pan while cooling.
My cookies did not crack on top. What happened?
Usually it is one of these: dough balls not rolled well, oven temp off, too much flour, or they baked too long. Try the double-roll tip (roll, rest 5 minutes, roll again) and pull them as soon as the edges are set.
Can I make them ahead for a party?
Yes. Bake a day ahead and store airtight. The cinnamon flavor actually blooms overnight. Or freeze dough balls and bake fresh the day of.
Can I make them gluten-free?
You can usually swap in a 1:1 gluten-free baking flour blend. Expect a slightly different spread and a more tender, sandy crumb depending on the brand.