Start by preheating your oven to 350°F (175°C).
Grease your 9x9 inch baking pan with butter or line it with parchment paper.
In a medium saucepan over low heat, melt the 1/2 cup of pure butter with coconut oil if using.
Remove from heat and whisk in the coconut sugar and cocoa powder until well blended.
Stir in the vanilla extract and add the lightly whipped eggs, mixing well after each addition until smooth.
In a separate bowl, whisk together the flour and salt, then gradually add to the wet ingredients, stirring just until combined.
Fold in the chocolate chips and walnuts until evenly distributed.
Pour the batter into the prepared pan and bake for 20-25 minutes, until edges are set.
Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before cutting.