Bring all ingredients to room temperature before mixing.
Mix soy milk and ground flaxseed in a small bowl. Set aside for 5 minutes to gel.
To a large mixing bowl, combine melted butter and walnut butter.
Add sugars and beat until combined. Stir in flax mixture and vanilla.
Add flour, oats, baking soda, baking powder, cinnamon, and salt (if using). Mix until a dough forms and no dry flour is left.
Stir in raisins.
Cover and transfer the dough to the fridge to chill for at least 30 minutes (up to 24 hours).
Take the dough out of the fridge and preheat the oven to 350°F.
Scoop about 2 tbsp of dough and roll into balls. Place 2-inches apart on a baking sheet.
When the oven is ready, place the cookies in the oven and bake 10 minutes. The edges should be just set but the center still soft when you remove them from the oven. They will look underdone but they continue cooking on the pan.
Drop the pan on the counter once after baking to flatten the cookies. Cool on the baking sheet for 3 minutes, then transfer cookies to a wire rack to finish cooling.
Notes
Gluten-Free: Use gluten-free oats and oat flour.Oil instead of butter: I have made these cookies with olive oil instead of butter and they were delicious! Use 40 grams olive oil + 15 grams soy milk (in addition to the 2 tbsp soy milk). You can try other oils as well, just be wary of strong-flavored oils as it will affect the flavor of the cookies.