Step 1

Preheat oven to 350F. Line a metal 8-inch square pan with parchment paper going both ways.

Step 2

In a small microwave-safe bowl, add chocolate chips and butter. Microwave in 30-second intervals, stirring in-between, until completely melted.

Step 3

Use a rubber spatula to transfer mixture into the bowl of a food processor. Add sugar and avocado and process for about a minute, or until fully combined, stopping and scraping down sides as needed. Wait until the mixture is room temperature (not hot) before moving to the next step.

Step 4

Add in eggs and vanilla and process for about 30 seconds (beating eggs helps with the crackly top). Add flour, cocoa powder, instant espresso powder, and salt and process only for a couple seconds, or until you don't see flour. Over-blending will make brownies hard. Fold in walnuts by hand with a rubber spatula. The batter will be very thick.

Step 5

Spoon into prepared pan and smooth top. Top with a pinch of flaky salt, if desired. Bake for 30 minutes, or until the middle is just set (the brownies will keep baking in the pan once out of the oven). If using a toothpick, it won't be clean. Let cool in pan for 20 minutes before slicing. Store in an air-tight container on the counter for a few days or in the refrigerator for longer. We enjoyed them right out of the fridge!