Combine melted butter, brown sugar, 3 tablespoons milk and salt in a medium microwave-safe bowl. Stir to combine.

Place in microwave and cook on high power for 1 minute. Stir well and return to microwave cooking another 1 minute on high. Mixture will vigorously bubble. Watch carefully to make sure it does not boil over sides of bowl

Remove from microwave and set aside to cool for 30 minutes, then proceed with recipe.

Place mashed avocado, softened butter and powdered sugar in the bowl of an electric mixer. Start with mixer on low speed and beat for 1 minute. Increase speed to medium and mix for another minute.

Add vanilla and cooled brown sugar/butter mixture and 1 tablespoon milk. Beat on medium speed for 5 minutes, scraping down sides of bowl with a rubber spatula every minute or so.

Icing should be creamy and spreadable. If it’s too stiff, add more milk and conversely, if too runny add powdered sugar, a little at a time until desired consistency is reached.