Preheat oven to 350 degrees F. Line 15 muffin cups.
Microwave the milk until hot and stir in the coffee granules. If not using buttermilk, add the vinegar at this point. Set aside and let cool to room temperature (you might have to refrigerate it).
In a small bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.
In the medium bowl of an electric mixer, beat the eggs until smooth. Add the oil and sugar; mix well. Add the vanilla.
On low speed, sift in half the flour mixture and mix just until combined. Add half the milk mixture and mix; repeat with the rest of the flour and milk.
Pour into prepared muffin tins and bake for 12-13 minutes, or until a toothpick inserted in the center comes out clean. *If you use espresso granules, the batter will be much lighter than how it appears in the picture (I used coffee granules).