Preheat the oven to 350°F and line the baking pan with parchment paper for easier removal. Lightly coat the paper with non-stick spray.
Melt the chocolate chips and butter in a small saucepan. Remove from the heat just as they melted to avoid burning the chocolate.
Pour the mixture into a bowl and add the sugar, milk, and vanilla extract. Mix well, then add the flour, cocoa powder, baking powder, and salt. Mix just until the batter comes together, then fold in the walnuts.
Pour the brownie batter into the prepared baking pan. Bake for 30 to 35 minutes or until a toothpick inserted in the center comes out with just a few moist crumbs and the brownies are pulling away from the sides of the pan.
Allow your fudgy vegan brownies to cool before slicing.
Notes
Mix the batter just until combined or when you no longer see streaks of dry ingredients. Overmixing can cause brownies to sink in the middle!
For easier removal, line the baking pan with parchment paper and use the overhang to lift the brownies out. Allow them to cool completely before slicing. Cut the vegan brownies with long strokes instead of a sawing motion.
Let the fudgy vegan brownies cool completely, then cover them with foil or plastic wrap. For the best texture, store the brownies at room temperature for up to 3 days. You can also keep the leftover brownies in an airtight container in the fridge for up to 5 days.