Butter an 8 by 8 inch pan and preheat the oven to 350° F.
Start by browning your butter. Place butter in a heavy saucepan over medium heat until melted. Continue to cook, swirling occasionally, until butter becomes brown. It will pop and sputter a lot at first, but then it will quiet down. It's ready when the popping has calmed down, there are brown specks at the bottom of the pan, and it smells toasty and nutty.
Add brown butter to a bowl and whisk in brown sugar. Allow to cool for a few minutes.
Add egg and vanilla, whisking thoroughly until batter is silky smooth.
Whisk together all purpose flour, teff flour, baking soda and salt. Add dry ingredients to butter mixture, folding until almost combined. Fold in chocolate chips.
Pour batter into prepared pan and smooth out the top.
Bake until edges are set and top is golden brown and crinkly, about 25-30 minutes.
Allow blondies to cool and set completely before slicing into squares. I cut mine into 16 squares, but you can make them any size you like!