Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan, or line it with parchment paper, leaving an overhang to easily lift the cake out later.

In a medium bowl, whisk together the flour, granulated sugar, baking powder, and salt.

In a separate large bowl, beat the room temperature butter until creamy. Add the egg and vanilla extract, mixing until well combined.

Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until just combined—be careful not to overmix.

Pour the batter into your prepared pan and spread it evenly. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let the cake cool completely in the pan.

In a large bowl, use an electric mixer to beat the softened butter and marshmallow fluff together until smooth and creamy.

Gradually add the powdered sugar, mixing on low speed until it's fully incorporated. Increase the speed to medium-high and beat for another 2-3 minutes until the frosting is light and fluffy.

Once the cake is completely cool, spread the marshmallow frosting evenly over the top.

Place the shredded coconut in a zip-top bag. Add a few drops of pink food coloring, seal the bag, and shake vigorously until the coconut is evenly colored.

Sprinkle the pink coconut generously over the frosted cake, pressing down gently to help it adhere.

Refrigerate the cake for at least 1 hour to allow the frosting to set. This makes cutting into clean bars much easier. Once set, lift the cake from the pan using the parchment paper overhang and cut it into bars.