Preheat oven to 350°F and grease a half sheet pan (18x13 inches).
In a stand mixer bowl or large mixing bowl, combine all purpose flour, sugar, salt, baking soda and baking powder.
In a medium mixing bowl, whisk together sour cream, eggs, vanilla extract and peppermint extract.
Melt butter, cocoa powder and instant coffee in a medium sauce pot over medium heat.
Once all melted and combined, whisk in the hot water. Cook just until the edges start to bubble, but DO NOT boil. Remove from heat.
Pour the chocolate mixture over the dry ingredients in the mixing bowl. Mix on low just until combined.
Add the sour cream and egg mixture and mix until fully combined and smooth.
Bump up speed and mix on medium for 30 seconds.
Pour cake batter into greased half sheet pan (18x13 inches).
Bake for 25-30 minutes until toothpick inserted in the center comes out clean. Rotate the cake half way through baking.
After you rotate the cake, make the frosting.