Preheat oven to 350°F. Line muffin tins with liners.
Sift flour, sugar, cocoa, baking soda, baking powder, and salt together in a large bowl.
In a separate bowl, whisk the egg, buttermilk, hot coffee, oil, and vanilla.
Pour the wet ingredients into the dry. Mix on medium speed for 2 minutes, scraping the bowl once. The batter will be thin.
Fill liners evenly. Bake 12–15 minutes until a toothpick comes out mostly clean. Cool completely.
For frosting: Beat butter and cream cheese until light and fluffy (2–3 minutes). Add pumpkin pie filling and mix.
Beat in powdered sugar, salt, and heavy cream until smooth. Whip on high for 2–3 minutes.
Frost cooled cupcakes and serve.