Place the raspberries, sugar, and lemon juice in a medium saucepan. Cook over low-medium heat, stirring often, until the berries soften and the mixture becomes thickened, about 8 to 10 minutes.

In a small bowl, stir the cornstarch and water together until smooth. Pour the slurry into the raspberry mixture and stir immediately. Continue cooking for 2 to 3 minutes, or until the filling thickens fully. Remove from the heat, mix in the vanilla, and transfer to a bowl to cool completely. Refrigerate if needed to hasten cooling.

Preheat the oven to 325°F (163°C). Line the bases of three 8-inch round cake pans with parchment paper, coat with cooking spray, and set them aside.

In a large mixing bowl fitted with a paddle attachment, combine the cake mix, instant pudding, eggs, coconut milk, and canola oil. Beat on medium speed for about 2 minutes, until the batter is smooth and thoroughly blended. Fold in the shredded coconut.

Divide the batter evenly between the prepared pans, smoothing the tops. Each pan should hold about 390 grams, or 13.75 ounces, of batter.

Bake for 22 to 25 minutes, until the cakes no longer wobble and the centers spring back lightly when touched. The tops and edges should be lightly golden. Let the layers rest in their pans for 15 to 30 minutes, then turn them out onto a wire rack and cool completely.

To prepare the frosting, beat the softened cream cheese and butter together in a large bowl until smooth. Add the icing sugar gradually, then blend in the vanilla essence, coconut milk, and salt. Beat only until the frosting is light and combined. Adjust the texture with a little more icing sugar or coconut milk as needed.

For the garnish, melt 1 teaspoon of butter in a large frying pan over low-medium heat. Add the coconut and stir frequently until it turns lightly golden, watching carefully so it does not burn. Transfer the toasted coconut to wax paper or paper towel and let it cool.

Set one cake layer on a cake plate or serving stand with the top facing upward. Spread a thin layer of frosting over the surface, then pipe a border of frosting around the edge using a ziplock bag with one corner snipped off. Spoon raspberry filling inside the border.

Add the second cake layer and repeat the frosting border and raspberry filling. Place the final cake layer on top with the top side facing down.

Spread a thin crumb coat of cream cheese frosting over the entire cake. Chill the cake in the refrigerator or freezer for 10 to 15 minutes.

Cover the chilled cake with the remaining frosting. Spoon extra raspberry filling over the top if desired, then press the toasted coconut over the outside of the cake to finish.