Preheat oven to 350 degrees and place parchment paper on a baking sheet.
Whisk together the flax seed and warm water. Let sit for 3-5 minutes, until it thickens.
Add the wet ingredients to a large mixing bowl: vegan butter, sugar, vinegar, vanilla and flax ‘egg’ - Cream everything together using a hand or stand mixer.
Add the dry - flour, salt, baking powder and optional cinnamon to the mixing bowl. Beat until creamy and fluffy.
Fold in the nuts and chips.
Cover and chill in the fridge for at least 15 minutes and up to a day ahead of time. (This step is optional.) I find that chilled cookie dough doesn’t spread or flatten quite as much, which is what some people like.
Scoop cookie dough onto baking sheet. Top cookies with a pinch of coarsely ground sea salt. Bake at 350 degrees for 11-14 minutes. Transfer cookies to cooling rack. Add a pinch more sea salt, if desired. Serve warm!