Combine the flour, sugar, cocoa powder, and baking soda in a medium sized bowl. In a separate bowl, beat the eggs and add oil, sour milk, and vanilla extract. Stir to combine and then stir in the hot water. Gradually add the dry ingredients into the wet ingredients, stirring well after each addition
Drop the whoopie pie batter by teaspoon onto greased cookie sheets and bake in the preheated oven for 7-10 minutes until the tops are dry and spring back to touch.
Cool the whoopie pies then frost with whoopie pie frosting (link to my Homemade Amish Whoopie Pie frosting below.) and enjoy! Keep scrolling for photos and notes.
Notes
To sour your milk you can also remove a tablespoon of milk from one cup of milk and replace it with one tablespoon of distilled vinegar. Stir the milk and let it set for ten minutes, then it is ready to use. If the whoopie pie batter spreads too much while being baked you can add another 1/4-1/2 cup flour to the batter. The batter should be thicker than cake batter but thinner than cookie dough. I prefer to use 1/2 cup olive oil and 1/2 cup vegetable oil. This makes a very tender and moist whoopie pie! Additional notes and photos below.