Step 1

Preheat: Preheat oven to 375°F (190°C). Line two baking sheets with parchment paper.

Step 2

Flax egg: In a small bowl, whisk together ground flax and water until smooth. Set aside to thicken.

Step 3

Oat flour: Add oats to a blender and process until it's a fine powder.

Step 4

Mix dough: In a large bowl, stir together peanut butter, coconut oil, and brown sugar. Mix until the mixture is a smooth liquid (no clumps of coconut oil should be visible). Stir in vanilla. Add oat flour, baking soda, baking powder, and salt. Stir until well combined. (Up until this point, you don't need to worry about over-mixing).

Step 5

Finish dough: Stir in the flax egg until well mixed. Add all purpose flour and stir just until combined. Gently fold in walnuts and chocolate.

Step 6

Bake: Scoop dough into golf-ball sized balls (about 3 tablespoons each). Use your hand to roll the balls until smooth, then gently press down to flatten the tops. Arrange dough over the two baking sheets. Bake one sheet at a time, until golden brown at the edges, about 12 minutes. Let cool on the baking tray (they will be quite delicate at first, and firm up as they cool). Sprinkle with flaky salt.