Preheat oven to 400 degrees. Line muffin tin with papers.
Add flour, sugar, chocolate chunks, cocoa powder, baking soda, and espresso powder to a large bowl. Whisk to combine.
Add sour cream, milk, vegetable oil, egg, and vanilla to a medium bowl and whisk well to combine.
Pour wet ingredients into dry ingredients and stir until combined.
Gently stir in half of the raspberries.
Spoon muffin batter into muffin liners, 2/3 full. Press remaining berries into tops of muffins.
Bake for 15 minutes or until a tester comes out mostly clean, with just a few moist crumbs.
Cool completely. Dust with powdered sugar, if desired.