After many efforts to contact the company that makes the product, they finally returned my emails and phone calls, responding:
“Please excuse the delay in our response. On behalf of Dr. Oetker Ltd., thank you for your inquiry regarding our Apple Cinnamon Muffin Mix. We always appreciate hearing from our Customers and we value the opportunity to respond to their questions. For high altitude baking, we recommend:
- Increase liquid; for each cup, add 2 to 4 tablespoons.
- Increase oven temperature by 25º F.
Enjoy and Good Luck!
NOTE: The question was asked, as the inquirer had bought several boxes for his son who lives in Boulder, Colorado. Boulder is a little higher in altitude than Denver which is around 1 mile high, hence the high altitude.