Position a rack in the lower third of the oven and preheat the oven to 350°F.
Melt the butter with the chocolate in a medium heatproof bowl set directly in a wide skillet of barely simmering water. Stir frequently until the mixture is melted and smooth.
Remove the bowl from the water and cool the mixture to lukewarm. Stir in the sugar, teff flour, salt, and vanilla, if using. Add all of the eggs and beat on high speed with the handheld mixer for about 2 minutes. The batter will get thicker and a little lighter in color, like chocolate frosting. Stir in the nuts, if using.
Scrape the batter into the pan and spread it evenly. Bake for 30 to 35 minutes, until a toothpick inserted in the center comes out fairly dry and clean (don’t worry; the brownies will be moist even if the toothpick is not).
Cool on a rack. Lift the foil ends to transfer the brownies to a cutting board. Cut into 16 squares. The brownies may be kept in an airtight container for 2 to 3 days.
Variation: Cocoa Teff Brownies
Cocoa brownies have a softer texture than chocolate brownies. Substitute ¾ cup (65 grams) unsweetened cocoa powder for the chocolate. Increase the butter to 13 tablespoons (185 grams), and increase the sugar to 1 cup plus 3 tablespoons (235 grams).
Excerpted from Gluten-Free Flavor Flours by Alice Medrich (Artisan Books). Copyright © 2014.