1. Preheat oven to 350°.
2. Combine first 4 ingredients in a medium microwave-safe bowl. Microwave at HIGH 30 seconds; stir. Microwave at HIGH 30 more seconds (mixture will bubble); whisk until smooth. Stir in meal, flour, and salt. Scrape mixture into center of a baking sheet covered with parchment paper. Spread into a 12-inch circle. Bake at 350° for 9 minutes, rotating pan after 4 minutes. Lift parchment and cookie onto a wire rack.
3. Place chopped bittersweet chocolate in bottom of a zip-top plastic bag. Microwave at HIGH 15 seconds. Snip a tiny hole in bottom corner of bag; drizzle over cookie.