Add softened room temperature butter and sugar to a bowl. Use a hand mixer or fork to mix them well together until they are fluffy.
Add the tahini and miso. Mix thoroughly. Finally, add the flaxseed meal, milk, and vanilla. Use a hand mixer to whisk together until totally smooth.
Add oat flour, all purpose flour, and baking soda to the same bowl. Mix well. Refrigerate the dough for 30 minutes.
Preheat the oven to 350 F.
Scoop 2 tbsp of cookie dough per cookie. Space them out a couple of inches apart (*important!) on a baking sheet lined with parchment paper. Top with dark chocolate. You could also mix the dark chocolate into the dough before you form the individual cookies.
Bake at 350 F for 18-22 minutes, but start checking on the cookies at 15 minutes. Add salt on top of the cookies when you check or add salt to the melted chocolate when the cookies come out of the oven.
