Mix eggs in mixer (or with hand mixer) until thoroughly mixed well on medium high speed.
Stream in oil slowly while continuing to mix.
Mix sour cream with milk with a fork. Add to wet ingredients.
Mix in coffee and vanilla.
Turning the mixer to low, add dry ingredients just until mixed. Finish folding in with spatula. You don't want to over-mix. Pour into prepared pans or cupcake liners.
Bake cupcakes 20 to 25 minutes. Cupcakes are done when the internal temperature is 205 F.
Bake an 8 inch layer cake 25 to 30 minutes. Cake is done at 210 degree. F.
Bake three six-inch layer cakes 23 to 26 minutes. Cakes are done at 210 degrees. F.
You can actually hear when your cake it done. If it's crackling it's still cooking off moisture.
Cool cakes before frosting.
If you decide to use a piping bag, make sure frosting is soft enough. If it's not moving through the bag easily, add a little hot water or milk a tablespoon at a time. I use a 1M piping tip.