Prepare the White Buttermilk Cake per the recipe directions in 9 x 13 inch pan. If using cake mix, prepare per the package directions in a 9 x 13 inch pan.
As soon as the cake is removed from the oven, use the end of wooden spoon or similar to poke holes over the surface of the cake.
Whisk together the sweetened condensed milk, 1 cup heavy cream, lime juice, 2 Tbsp lime zest and 1 tsp pure vanilla. Add a few drops of green food coloring, if desired.
Pour the key lime filling over the top of the cake and into the holes.
Spread evenly into the holes. Chill completely.
Whip the remaining 2 cup heavy cream, 1 tsp vanilla and 1/3 cup granulated sugar until stiff peaks form.
Frost the top of the cake.
Sprinkle with the remaining lime zest, toasted sliced almonds and grated white chocolate. Store chilled.