1. Preheat your oven to 350°F (175°C), grease 4-inch or 6-inch cake pans, and line the bottoms with parchment paper.
2. In a medium-sized bowl, whisk together 1 1/2 cups of all-purpose flour, 1 1/2 teaspoons of baking powder, and 1/4 teaspoon of salt. Set aside.
3. In a large mixing bowl, beat 1/2 cup of softened unsalted butter until creamy. Gradually add 1 cup of granulated sugar and continue to beat until light and fluffy.
4. Add two large eggs, one at a time, beating well after each addition, then mix in 1 teaspoon of vanilla extract or another flavoring of your choice.
5. Gradually add the dry ingredients to the butter mixture, alternating with 1/2 cup of milk, starting and ending with the flour mixture. Mix until just combined.
6. Divide the batter evenly between the prepared pans, and bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.
7. Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.
8. In a separate large mixing bowl, beat 1 cup of softened unsalted butter until light and fluffy to prepare buttercream frosting.
9. Gradually add 4 cups of powdered sugar, one cup at a time, until fully incorporated. Add 1/4 cup of heavy cream and 1 teaspoon of vanilla extract and beat until the frosting is smooth and fluffy. Adjust consistency with milk if too stiff, or chill if too soft.
10. Personalize the buttercream with optional food coloring, or add ingredients like chocolate, fruit puree, or coffee to create unique flavors.
11. Level the tops of the cooled cakes using a serrated knife if needed to ensure even layers.
12. Place one cake layer on your serving board, spread a thin layer of buttercream over it, and stack the second cake layer on top. Apply a thin crumb coat of buttercream over the entire cake and chill for 20-30 minutes.
13. After the crumb coat is set, apply a thicker, even layer of buttercream to cover the cake completely.
14. Chill the frosted cake for 20-30 minutes to firm up the layers before decorating.
15. Decorate your Bento Cake by using piping bags and tips to create designs like rosettes, swirls, or messages. Add edible decorations such as sprinkles, fondant shapes, or dustings of powdered sugar.
16. Package the completed cake in a bento box for an authentic touch or display it on a cake stand for serving.
17. Store any leftovers in the bento box, cover with the lid, and refrigerate for up to three days, allowing the cake to come to room temperature before serving again.
18. For advance preparation, bake the cake layers and prepare the buttercream frosting up to two days ahead, storing cakes wrapped in plastic at room temperature and frosting in the refrigerator. Decorate before serving.
19. Serve the Bento Cake in the box or on a small stand, use a sharp knife for clean slices, and pair with complementary beverages like tea or coffee.