Make the Cake:

1. Preheat the oven to 350°F. Grease and flour a 9×13-inch pan or two 8-inch round pans.
2. In a large bowl, mix together the cake mix, buttermilk, oil, eggs, lime zest, coconut extract, and vanilla. Stir until just combined—avoid overmixing.
3. Fold in the shredded coconut for a burst of texture in every bite.
4. Bake according to box directions, then let the cake cool completely before frosting.

Make the Frosting:

1. In a dry skillet over medium heat, toast the shredded coconut for 2–3 minutes or until golden and fragrant. Set aside to cool.
2. In a large bowl, beat the butter until smooth and creamy. Add lime zest, lime juice, and coconut extract.
3. Slowly mix in the powdered sugar. Add the heavy cream a tablespoon at a time until you reach a smooth, spreadable consistency.
4. Stir in ¼ cup of the toasted coconut.
5. Frost the cooled cake and finish with a sprinkle of the reserved toasted coconut on top for extra flavor and a pretty finish. Add additional sliced limes, if desired.