homemade double chocolate mint filled Oreos 
from vanillasugarblog.com

Cookie base:
7 TB unsalted butter, room temp
½ cup sugar
3 TB brown sugar
3/4 ts salt
¾ cup double Dutch DARK cocoa powder (+more for dusting board for rolling dough)
¾ cup all purpose flour
½ ts baking powder
¼ ts baking soda
1 ts pure vanilla extract
2 egg yolks

mint filling:
4 TB unsalted butter, room temp
1 + ¼ cups powdered sugar, sifted
¼ ts pure vanilla extract
¼ ts (or more) pure mint extract
a pinch of salt

Cook notes:
If you can’t find double dutch dark cocoa powder then use regular DARK cocoa powder but you might need more than ¾ cup; possibly a cup? 
Not sure since I haven’t made it with regular cocoa powder. I highly suggest investing in some double dutch dark cocoa powder. King Arthur Flour sells it.
If you don’t want mint filling then you substitute the mint extract for vanilla extract; use ¾ ts vanilla extract. Do a taste test of filling.
I used 4 inch cookie cutters, feel free to use 2 inch or whatever shape you desire.

Sift the flour, cocoa powder, baking soda, salt, baking powder; set aside.
Using a mixer cream butter and both sugars. Add in the egg yolks.
Make sure to scrape down the sides of the bowl. Next add in the dry mixture (the flour mixture). And mix until combined. It will be a thick, sticky dough. 
Place dough in plastic wrap, shape into a ball. Cover with plastic wrap and flatten into a disc.

Chill dough for at least a couple hours. When ready to use, let it sit at room temp for 20 minutes or when it’s ready/easy to roll. 
 Don’t let dough get too warm; we want it to stay fairly cool.
Preheat oven to 350 degrees. Line your cookie sheets with parchment paper.
Dust your board and rolling pin with cocoa powder, and roll out dough to about 1/8 of an inch thickness
Cut out circles with a 4” or 2" round cutter or whatever shapes you desire. Use a thin metal spatula under the dough to move it to the cookie sheet.

Place a couple inches apart on cookie sheet. They don’t spread much, but if your dough is too warm they might. 
 If you think your cookie dough got too warm then just pop them back in the fridge before baking.
Knead the scraps of dough together, re-roll and cut out until all or most of the dough is used.
Bake 10 - 12 minutes, or until almost firm. You need to let these cool on the cookie sheet (about 8-10 minutes); they need to set up.

Mint filling:
Using a hand or stand mixer cream together butter, powdered sugar, vanilla, mint, and salt on medium speed 5-7 minutes until light, creamy and fluffy.
I found that using a pastry bag fitted with a plain tip worked best. But you can use a ziploc bag with a hole in the corner or simply use a spoon/knife to place filling into center of cookie.

Should make:
12-14 (4 inch cookies)
22-24 (2 inch cookies)

Store in airtight container. Keeps 2 days if that.