1. Preheat the oven to 325°F and grease and flour a bundt pan.
2. In a mixing bowl, combine the cake mix, vegetable oil, pineapple juice, and eggs using an electric mixer until the batter is smooth.
3. Pour the batter into the prepared bundt pan and bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
4. Allow the cake to cool slightly. Meanwhile, prepare the glaze by heating powdered sugar, pineapple juice, and butter over medium-low heat until the butter melts.
5. Poke holes in the warm cake and pour the glaze over it, allowing it to soak through before the cake cools completely.
6. To make the filling, cook sugar, cornstarch, milk, and lemon juice in a saucepan over medium heat until thickened. Remove from heat, add butter, and let it cool.
7. For the frosting, mix mascarpone, icing sugar, and vanilla essence. Whip in the cold whipping cream until stiff peaks form, then fold in the drained crushed pineapple.
8. Assemble the cake, layering it with the filling and topping it with the frosting. Decorate as desired.