Preheat oven to 350°F/180°C. Line a mini muffin pan with paper liners. Set aside.
Melt butter in a medium saucepan. Remove from heat and add in chocolate and salt. Whisk until melted and smooth (if it doesn’t completely melt, cook on low heat for a few more seconds). Transfer to a large bowl. Add sugar and whisk until well combined. Add eggs and whisk until combined and shiny. Add flour and cocoa powder and, using a rubber spatula, fold just until combined and no more flour is visible.
Store brownie bites at room temperature in an airtight container for up to 2 days or in the refrigerator for up to 5 days. Brownies can be frozen for up to 2 months. Thaw on the counter, still covered, or overnight in the fridge.