Preheat oven to 350F/ 176C. Line an 8x8* pan with parchment paper with overhang and grease the pan with cooking spray.
To make flax egg - In a small bowl, whisk ground flax seed and 5 tablespoon of water. Set aside.
To make simple syrup - In a sauce pan over medium heat, add cane sugar and ½ cup water. Stir to combine, heat for about 6-8 minutes, and the sugar has dissolved completely. (DO NOT add more water. DO NOT let come to a boil or the mixture will evaporate)
While waiting, in a large bowl, add in the flour*, cocoa, powdered sugar, espresso powder (if adding), and salt. Whisk together.
Once simple syrup is ready, while hot, add it along with vegetable oil, vanilla, and flax egg. Combine with a spatula just until combined. Do not overmix. Batter should be fudgy and pourable. See video for reference. If adding walnuts, add now along with ½ cup vegan chocolate chips. Fold to combine. Do not over mix.
Pour batter into greased pan. Top with remaining ¼ cup chocolate chips. Bake for 35-40 minutes. A toothpick may not come out clean since they are fudgy.
Remove from the oven and let cool completely before slicing. The brownies need time to set up. For a firmer brownie, place in fridge. Slice in 16 equal sized pieces (or desired size)
Store leftovers in an air tight container.