Preheat 350*F. Line a baking sheet with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, cream non-dairy butter and brown sugar until light and fluffy. Then, add peanut butter and mix on low until combined.
8 tablespoon Non-Dairy Butter, 1 Cup Brown Sugar, tightly packed, ½ Cup Natural Creamy Peanut Butter
Add non-dairy milk and vanilla and mix on low until combined.
¼ Cup Non-Dairy Milk, 2 teaspoon Vanilla Extract
Next, add flour, baking soda, and salt, and mix until just combined. Then, remove the bowl from the mixer and add the marshmallows. Use a rubber spatula to mix the marshmallows into the cookie dough until they are distributed.
1 ⅓ Cup All-Purpose Flour, ½ teaspoon Baking Soda, ¼ teaspoon Kosher Salt, 1 Cup Mini Vegan Marshmallows
Use a 3-tablespoon scoop to scoop 6 dough balls, evenly spaced, onto a parchment-lined baking sheet. Add 2-3 extra marshmallows to the top of each dough ball, gently pressing the marshmallow into the cookie dough. This will also gently press the cookie dough out to help it spread.
Bake the cookies in a 350*F oven for 13-15 minutes or until the edges are golden brown. Allow the cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to continue cooling. Repeat with the remaining cookie dough.