Prepare the blended oats, by placing 3½ cups of rolled oats into a food processor and blender and process until the oats reach the consistency of flour. Measure 2 ½ cups of the blended oats and place them in a large mixing bowl.
Prepare the blended nuts, by placing 2½ cups of nuts in a blender or food processor. Pulse the nuts until broken down into very small pieces, being careful to not overprocess. Measure1½ cups of the blended nuts and place them in the same bowl as the oats.
Add the flour, baking powder, baking soda, and salt to the oats and nuts and mix until well combined. Add the chocolate chips and grated chocolate bar and toss with the dry ingredients to lightly coat with flour. Set this mixture aside.
In a large mixing bowl or stand mixer, cream the butter with the granulated and brown sugar together until fluffy and light in color, about 7-8 minutes. Add the eggs and vanilla and beat until well combined.
Add the dry ingredients to the creamed butter and fold together until the flour is fully moistened and just combined. Cover the dough and refrigerate for at least 30 minutes or up to 48 hours.
When ready to bake the cookies, preheat the oven to 375℉. Line a baking sheet with parchment paper.
Remove the chilled dough from the refrigerator. Use a medium cookie scoop or 1½ tablespoons for each cookie and then gently roll into even balls. Place the cookie dough onto the prepared baking sheet, spaced 2 inches apart.
Bake the cookies for 6-7 minutes, until the edges are lightly brown and the centers are just a bit soft.
Cool the cookies on the cookie sheet for a minute or two before transferring them to a cooling rack to cool completely.
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Notes
Oats: Either quick cook or old-fashioned rolled oats, not steel-cut oats. Grated Chocolate: To grate your chocolate, use a hand grater, box grater, or food processor and grate the chocolate bar into small shreds. It works best if your chocolate bar is cold before grating.Chilling Cookie Dough: Do not skip the step of refrigerating the dough for at least 30 minutes to keep the cookies from spreading too much. You can bake the cookies after 30 minutes or store the dough in the refrigerator for up to 48 hours before baking. If you find that your dough is too hard to scoop after chilling, let it set out at room temperature for 10 minutes, this can happen when chilled longer than a few hours. Storing Cookies: Store cookies in a sealed container at room temperature for up to 3 days. They will also last in the refrigerator for up to 7 days. Freezing Cookie Dough: Prepare the recipe as directed. Once the cookies have been rolled into balls, place them onto a rimmed cookie sheet that has been lined with parchment paper. Freeze for 1 hour, or until solid. Transfer the balls to a freezer-safe storage bag and store them in the freezer for up to 3 months. Bake at 375 degrees F for 8-10 minutes directly from the freezer.