First, make your flax egg. Add your ground flax seed and water to a medium size bowl. Stir and then let this sit for 10 minutes to make an "egg" consistency.
While you are waiting for the flax egg, preheat the oven to 350 F and line a cookie sheet with parchment paper.
Once your flax egg is ready, add the remaining ingredients to the bowl (minus the sprinkles and peanut butter cups) and mix well. NOTE: runny peanut butter is imperative for this recipe! I recommend a new jar of natural peanut butter, mixed very well, or if you have a jar stored in the fridge, take it out and let it sit at room temp for a while until its soft and runny. Dry or hard peanut butter will not work.
When you first start mixing, the dough will look extremely wet. Keep mixing! Mix until you have a dough consistency. The dough should be malleable but not sticky, and definitely not dry. See my photos for reference!
Using a medium size ice cream or cookie scoop (mine is 5 cm, or use about 2 & 1/2 tbsp per cookie) roll into balls and place on the lined cookie sheet. You should have 10 cookies.
Bake for about 11 minutes on the middle rack. The cookies should be lightly golden brown on the bottom and only slightly golden on the sides. You don't want to overbake these!
Once you remove the cookies from the oven, let them cool for 5 minutes.
Then, gently press a mini vegan peanut butter cup in the center of the cookies. Make sure to press gently and not too hard or too far because this can cause the cookies to break. A little breakage is normal but you don't all want the sides to break open. The cups will melt a little so again, it's not necessary to press hard.
Work pretty fast as the cups will start melting. As soon as all the cups are pressed into the cookies, transfer the cookies to a plate and freeze them for 5 minutes so the chocolate can set.
After the chocolate has set, leave the cookies at room temp until ready to serve (they shouldn't melt unless it's too hot in the house. If so, put them in the fridge).
Top with your favorite festive sprinkles and enjoy! I like to store these at room temperature so they stay soft.