Plain full-fat Greek yogurt can replace the sour cream. Avoid nonfat yogurt because some fat helps give the cake its soft, rich texture.
Instant espresso powder provides concentrated coffee flavor without adding excessive liquid to the frosting. Instant coffee can work in a pinch, but the flavor may be milder.
For a sweeter coffeehouse-style finish, sprinkle the top with cinnamon or decorate individual slices with a few chocolate-covered coffee-style candies made with halal-suitable ingredients.
This easy pumpkin cake is especially delicious alongside coffee, tea, chai, or a glass of cold milk.