Step 1
Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9-inch square pan.
Step 2
Cream butter and sugar together in a large bowl. Beat in eggs one at a time; stir in vanilla extract.
Step 3
Combine flour and baking powder in a separate bowl; add to the creamed mixture and mix well. Mix in the coconut milk until batter is smooth. Scrape into the prepared pan and smooth the top flat.
Step 4
Bake in the preheated oven until the top springs back when lightly touched 30 to 40 minutes. Cool on a wire rack for 5 minutes. Run a table knife around the edges to loosen. Invert carefully onto a cooling rack. Let cool about 30 minutes.
Step 5
Meanwhile combine crushed pineapple juice and cornstarch in a saucepan. Whisk until cornstarch is smooth. Heat over medium heat stirring constantly until filling has thickened and just barely starts to boil. Remove and set aside to cool.
Step 6
Cream confectioners' sugar and shortening together in a large bowl until light and fluffy. Beat in vanilla extract. Gradually add coconut milk beating until smooth; you may need to use more or less milk depending on the desired thickness of the icing.
Step 7
Cut the cooled cake in half to form two 4 1/2x9-inch pieces. Spread pineapple filling on top of one half. Place the other half top-side down on top of the filling. Frost the sides and top with icing then sprinkle coconut all over icing pressing gently so it sticks.