Vanilla Buttermint Poke Cake with Buttercream Frosting

This sweet mint pie looks and tastes just like Christmas. This poke pie has everything you love in terms of texture, but it's also deliciously soft and minty with a gorgeous palette of pure white. Finish your holiday dinner with a mint pie - shaped like a cake!
Prepare the cake according to the instructions on the 9x13-inch cake box. Let the cake cool for 20 minutes.Using a wooden dowel or the round handle of a wooden spoon, make holes all over the surface of the pie; be careful not to pierce all the way to the bottom of the pie pan.Place the crushed white chocolate in a medium-sized glass bowl. Heat the heavy cream in a small saucepan over medium-high heat until it boils (do not bring to a boil). Immediately pour hot cream over the crushed chocolate; beat until the chocolate is melted and the mixture is smooth. Whisk with mint extract. Pour the warm chocolate mixture over the finished cake, don't forget to fill the holes with the melted mixture and spread the excess chocolate mixture evenly over the surface of the cake. Let the cake stand for 30 minutes.Beat the butter and salt on medium speed with an electric mixer for 1-2 minutes or until creamy. Gradually add the powdered sugar alternately with 6 tablespoons of milk, whisking on low speed until smooth after each addition. Add vanilla. If desired, whisk in the remaining 1 tablespoon of milk, 1 teaspoon at a time, until the frosting has the desired consistency. Spread the mixture evenly over the cake; sprinkle evenly with crushed mints.