I don't have cream of tartar. Would it be possible to substitute in baking powder and baking soda? (Like as suggested here: https://whatscookingam...

Wait. Does the recipe call for either baking powder or soda? Baking powder is essentially a mix of soda and cream of tartar - the tartar provides the acid the soda needs to activate. SO my experience is you can use cream and tartar together with soda to replace baking powder - not the other way around. It depends on the purpose of the ingredients I have not seen the recipe. Good luck