Preheat oven to 425˚F (220˚C).
Puree cooked lentils and water together using a blender or food processor until smooth. Reserve.
In a large mixing bowl, combine both flours, baking powder, salt, sugar, garlic powder, and pepper with a whisk.
Grate cold butter into the flour and mix in. Stir in the pureed lentils.
Using your fingertips, rub butter and pureed lentils into dry ingredients until mixture resembles crumbs. Work quickly so that the butter does not melt.
Make a well in the center and pour in ⅔ cup chilled buttermilk and the dill. Stir just until the dough comes together. The dough will be very sticky.
Turn dough onto floured surface, dust top with flour and gently fold dough over on itself four or five times.
Press into a 1 inch thick round. Cut biscuits into eight portions. Place biscuits on baking sheet.
Whisk together 2 Tbsp of buttermilk and egg. Lightly brush the top of each biscuit.
Bake for 15-20 minutes, biscuits should be golden on top.
