Chocolate Mint Fudge Sandwich Cookies

In a medium bowl, stir together the all-purpose flour, cocoa powder, and baking powder.
In a large mixing bowl, beat the softened butter with a mixer on medium speed for about 30 seconds.
Add the granulated sugar and oil.
Continue to beat until well combined, scraping the sides of the bowl as needed.
Beat in the eggs and vanilla extract until fully combined.
Gradually beat in the flour mixture.
Cover the dough and chill it for 1 hour or until it's easy to handle.
Preheat your oven to 350°F (175°C).
Shape the dough into 1-inch balls and place them about 2 inches apart on an ungreased cookie sheet.
Dip the bottom of a glass in additional sugar and slightly flatten each ball.
Bake for 7 to 9 minutes or just until the cookies are firm.
Remove them and allow them to cool on a wire rack.
For the filling, in a small saucepan, combine the remaining ingredients.
Cook and stir over medium heat until the chocolate is melted, then let it cool.
Spread the filling on the bottoms of half of the cookies, using about 1 teaspoon for each cookie.
Top with the remaining cookies, bottom sides down.