1. Preheat the oven to 350°F. Line an 8-inch square pan with a piece of parchment paper, leaving an overhang on two opposite sides. Set aside.
2. In a medium bowl, whisk together the nut or seed butter, maple syrup, applesauce, and vanilla.
3. To the nut butter mixture, add the cocoa powder, coconut flour, baking soda, and sea salt. Whisk to combine, ensuring that there are no dry lumps of cocoa in the batter.
4. In a double boiler, melt half of the chocolate chunks. Vigorously stir the melted chocolate into the brownie batter until fully incorporated.
5. Scrape the brownie batter into the prepared baking pan. Smooth the batter out evenly with a spatula, pushing it into the edges and corners of the pan.
6. Scatter the reserved chocolate chunks and rough-chopped nuts over the top. Slide the pan into the oven, and bake the brownies until the top is slightly firm and appears dry and lightly cracked, about 27 to 30 minutes.
7. Cool the brownies completely in the pan set on a wire rack. Then, cover the brownies and place them in the refrigerator for at least 1 hour. This step is crucial. The brownies will not cut neatly unless they get adequate cooling time.
8. I recommend running a chef’s knife under hot water and drying it off right before slicing the brownies.