Whisk together yolks, sugar, and a pinch of salt in a bowl until combined well, then add hot cream in a slow stream, whisking until combined.
Transfer mixture to saucepan and cook over moderately low heat, whisking constantly, just until it thickens. Add in the vanilla and chocolate chips and whisk until the chocolate is melted and fully incorporated. Set aside to cool.
Beat remaining cream, 3 T. sugar, and peppermint oil in a bowl with an electric mixer until it holds stiff peaks. Divide Whipped cream in half and set other half aside.
Whisk one fourth of cream(of a half that was set aside) into chocolate custard to lighten, then fold in remaining cream gently but thoroughly. Spoon into a piping bag and set aside. Place the other half of the whipped cream in a separate piping bag.
Crush the mint cookies into small chunks.
Pipe a layer of chocolate mousse in the bottom of 6 small glass dishes. Pipe a layer of the mint cream on top of each chocolate mousse layer. Sprinkle about 1 T. of crushed cookies in each glass. Pipe another layer of chocolate mousse on top of the cookies. Pipe a swirling of mint cream on top of each glass and place a piece of cookie and a mint sprig on top of the cream. Let set in the refrigerator for 2-3 hours. Serve well chilled.
Recipe by The Kitchen McCabe at https://www.thekitchenmccabe.com/2014/03/04/mint-chocolate-mousse-cookies-cream-parfaits/