Devil Dogs Recipe from Good Grief Cook

Ingredients

• 2 cups all purpose flour
• ½ cup unsweetened cocoa powder
• 1½ teaspoon baking soda
• ½ teaspoon instant espresso powder, optional
• ½ teaspoon salt
• ½ cup unsalted butter, room temperature
• ½ cup sugar
• 1 egg, room temperature
• 1 teaspoon vanilla
• 1 cup milk, room temperature

Ermine Butter Cream Filling

• ½ cup all purpose flour
• ½ cup milk
• ¼ teaspoon salt
• 1 cup powdered sugar
• ½ cup unsalted butter
• ½ cup shortening
• 1 teaspoon vanilla

Directions

1. Heat oven 425F. Line baking sheets with parchment.
2. In large bowl, sift flour, cocoa powder, baking soda, espresso powder and salt; whisk it to blend and set aside.
3. In another bowl, beat butter and sugar for 5 minutes. Beat in egg and vanilla. Add ⅓ of dry ingredients alternating with half the milk beating well after each addition and scraping down bowl as needed.
4. Spoon batter into a zippered plastic bag; seal bag. Snip off a ½-inch piece of one corner.
5. Pipe batter into 3-inch logs about 1½ to 2-inches wide and 2-inches apart on prepared baking sheets.
6. Bake 8 minutes. Cool.
7. Turn half the cakes over and pipe or spread flat sides with cream filling.
8. Cover with remaining cakes, flat side down.
9. For the filling: In a small saucepan over medium-low heat whisk flour, milk and salt until blended and no lumps remain.  Cook mixture, stirring with a wooden spoon, until it thickens, pulls away from the sides of the pan and forms a smooth ball. This will take at least 5 minutes of hard stirring with the wooden spoon until the dough leaves a skin in the pan and is not sticky. 
10. Transfer dough to a bowl. Let it cool for 5 minutes. Add powdered sugar; stir it in until it looks smooth and dough has loosened up. It will appear more liquid.
11. In another bowl, beat butter and shortening until blended. Add vanilla and beat well. Gradually add sugar mixture, 1 tablespoon at a time, beating until mixture is smooth, thick and fluffy.