To make the crust, mix butter, cocoa, nibs, sugar, salt, vanilla in a medium bowl. Add flour and mix until blended. Press the dough evenly over the bottom and up the sides of a 10 or 11-inch tart pan with a removable bottom. Generously prick the bottom and sides of the crust with the tines of a fork. Bake in the lower third of an oven preheated to 350° F until the crust feels firm to the touch, about 20 to 25 minutes. Cool completely.
Combine sugar and butter in the bowl of a standing electric mixer. Stir slowly with the paddle attachment until the butter is no longer visible. Add extracts, schnapps (if using), and heavy cream, stirring slowly until the powdered sugar is completely incorporated. Once mixture comes together, beat on medium speed for another minute or so until it forms a smooth, thick paste.
Scrape the peppermint filling into the cooled tart crust and spread it evenly to the edges, doing your best to smooth the top. Refrigerate until the filling hardens slightly, about 30 minutes.
For the ganache, place chopped chocolate in a measuring glass with a pour spout; set aside. Bring cream to a boil over medium heat. Pour hot cream over the chocolate; without stirring, let the cream-chocolate mixture sit for 2 minutes. After 2 minutes, stir slowly with a rubber spatula until the mixture is smooth and glossy.
Acting quickly, pour ganache over the peppermint filling. Carefully pick up the tart pan, tilting and rotating to spread the ganache to the tart’s edges as needed. If desired pop any large bubbles that form with a toothpick.
Refrigerate uncovered until set, about 30 minutes. Serve chilled or at room temperature.