Preheat your oven to 350 degrees Fahrenheit. Line two cupcake pans with 18 paper liners.
In a large bowl, combine chopped bittersweet chocolate, cocoa powder, and 3/4 cup hot water. Whisk until the mixture is smooth and all of the chocolate has melted. Place this mixture in the refrigerator to chill for about 20 minutes.
In a large bowl combine flour, sugar, salt, and baking soda.
When the chocolate mixture has cooled, whisk in 6 tablespoons vegetable oil, 2 large eggs, 2 teaspoons vinegar, and 2 teaspoons vanilla extract.
Combine the dry ingredients with the wet and whisk until all of the ingredients are incorporated together.
Place an Oreo cookie on the bottom of each cupcake liner.
Pour batter over each cookie and fill each cupcake liner about 3/4 of the way full. You should get about 18 cupcakes.
Bake for 17-18 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Cool on a wire rack.
While the cupcakes are baking, prepare the frosting. In a small sauce pan combine 5 tablespoons flour with 1 cup cold milk. I used 1%. Stir and whisk the mixture constantly over medium low heat until it becomes really thick. Place this mixture in the refrigerator or freezer for about 10 minutes so that it cools completely.
When the flour/milk mixture has cooled completely, cream together butter and sugar with your mixer. When the sugar is well incorporated into the butter, add in vanilla and mix for 30 seconds longer. Add in the thickened milk/flour mixture and mix on low for about 30 seconds. Then turn the mixer to high and mix for about 3 minutes, or until the frosting is light and fluffy, much like whipped cream. If the consistency isn't like whipped cream, keep mixing! Add in 1 cup crushed Oreos and mix for about 30 seconds.
To frost the cupcakes, place the frosting in a ziplock bag, snip the corner, and pipe frosting onto each cooled cupcake. Top with an additional Oreo for garnish.