Preheat oven to 325°. Line an 8×8-inch glass or metal baking pan with foil or parchment paper, leaving a 2-inch overhang and apply nonstick spray.

Melt butter in a small saucepan over medium heat or in microwave. Let cool slightly, then pour into medium bowl. Whisk stevia, coconut sugar, cocoa, salt and coffee into melted butter. Add vanilla, then add milk and applesauce. Mix well. Beat egg in separate bowl and then add to mixture, blending well.

In a small bowl, combine flour, baking soda, baking powder and flax seeds (if using). Add dry ingredients to wet ingredients, and stir until just combined (do not over-mix). Fold-in chocolate chips and chopped nuts, along with cocoa nibs, if using. Scrape batter into prepared pan; smooth top. Bake until top begins to crack and a toothpick inserted into the center comes out with a few moist crumbs attached, about 19–25 minutes. Transfer pan to a wire rack and let cool completely. Using foil overhang, lift brownies out of pan; transfer to a cutting board or keep inside of pan. Cut into 12 squares. Store in a sealed glass container for about a week in the refrigerator or up to several months in the freezer.

For a completely sugar-free version, use 1½ tablespoons of stevia only. Note, however, with some people stevia leaves a bitter aftertaste.