Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
Melt butter and dark chocolate in a heat-safe bowl over simmering water or in the microwave. Stir until glossy.
Whisk in brown sugar and granulated sugar until incorporated.
Beat in eggs, one at a time, then add alcohol-free vanilla extract.
Whisk gluten-free flour, cocoa powder, baking powder, and salt in another bowl.
Gradually add dry ingredients to the wet mixture, blending until smooth.
Fold in mini chocolate chips.
Scoop dough into 12 mounds per baking sheet and flatten slightly with a fork.
Bake for 8–10 minutes (cookies will rise during baking). Cool completely.
For mint frosting, beat butter and powdered sugar until light. Add alcohol-free peppermint extract and green coloring, mixing in 1 Tbsp milk/cream until creamy.
For ganache, heat cream until warm, then pour over chocolate chips. Let sit 2–3 minutes, stir until smooth, and chill 15 minutes.
Spread frosting on cooled cookies and drizzle with ganache before serving.