Preheat oven to 350°
Prepare 2 baking sheets by lining with parchment paper or silicone mats.
In a medium bowl, whisk together the flour, cocoa, salt and baking powder. Optional: sift ingredients together to remove any lumps in the cocoa powder and flour.
Melt the chocolate and coconut oil gradually over a pot of simmering water or in a microwave (note: the coconut oil is optional). Cool slightly.
Using a stand mixer with the paddle attachment, begin creaming the butter and granulated sugar until light and fluffy (2 - 4 minutes on medium speed). Scrape the bowl as needed.
Add the eggs one at a time to the bowl, mixing between each addition. Scrape the bowl as needed.
Add the cooled, melted chocolate to the mixing bowl. Mix on medium speed, scraping the side of the bowl occasionally, until the chocolate is incorporated.
Add the room temperature milk to the mixing bowl. Mix on low speed until combined.
Add the flour mixture and mix on low speed until combined.
Stir in chopped walnuts.
Scoop the dough onto the parchment-lined baking sheets using a small cookie scooper (approximately 2 tablespoons per cookie). Leave approximately 2 inches of space between each cookie.
Bake cookies for 9 - 10 minutes, or until tops and edges of cookies are browning.
Let cookies cool on the baking sheets for 5 to 10 minutes, then transfer them to a wire rack to cool completely.