Grease a 9-inch tart pan or pie pan.*

Using an electric mixer, beat the butter and sugar until fluffy. Mix in the vanilla. Add the flour and salt, and mix until combined. Add the milk and beat until dough is mixed and holds together when pressed between your fingers.

Press the dough into the bottom and up the sides of the prepared pan. Using a fork, prick holes over the bottom of the tart dough. Place the pan in the refrigerator for about 10 minutes.

Place the pan on a baking sheet. Bake for 15 to 20 minutes, or until lightly browned around the edges and set in the center. If the edges are getting too brown, cover with foil and continue baking. Cool completely.

Place the chocolate in a microwave-safe bowl. Heat in the microwave at half-power in 30-second increments until the chocolate melts when stirred. Allow to cool to room temperature.

Using an electric mixer on medium speed, beat the mascarpone, cooled chocolate, and liqueur until smooth and creamy.

Transfer the filling to the cooled tart crust and spread evenly. Place the tart in the refrigerator for at least 2 hours.

Garnish with sweetened whipped cream and chocolate shavings when serving.