Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
Mix dry ingredients: In a medium bowl, whisk flour, baking powder, baking soda, and salt.
Cream butter and sugar: In a large bowl, beat butter and brown sugar until fluffy. Add eggs one at a time, then vanilla and espresso powder.
Combine: Add dry ingredients alternately with milk and sour cream. Mix until just combined.
Bake: Divide batter between liners and bake 18–20 mins. Cool completely.
Make the frosting: Beat butter until creamy. Gradually add powdered sugar, then caramel sauce, salt, and cream until fluffy and smooth.
Decorate: Pipe or spread frosting on cooled cupcakes. Drizzle with caramel and a dusting of espresso powder if desired.