Preheat oven to 350 °F (175 °C). Grease and flour two 8-inch round cake pans.
Whisk together flour, baking powder, and salt in a medium bowl.
Cream softened butter and granulated sugar until light and fluffy, about 3–4 minutes.
Beat in eggs one at a time, then mix in vanilla extract.
Alternate adding the flour mixture and milk in three additions, beginning and ending with flour. Mix until just combined.
Divide batter evenly between prepared pans.
Bake for 28–32 minutes until a toothpick comes out clean.
Cool in pans 10 minutes, then transfer to wire racks to cool completely.
Prepare buttercream by beating softened butter until smooth, gradually adding powdered sugar, heavy cream, vanilla, and pink gel food coloring.
Level cake layers, stack with buttercream between layers, crumb coat, and refrigerate 20–30 minutes.
Apply final coat of pink buttercream and smooth with a bench scraper.
Roll out white fondant and cut out Hello Kitty face shape using a template. Add black fondant eyes, whiskers, yellow nose, and pink or red fondant bow.
Place fondant decorations on cake, add finishing touches such as piped borders, sprinkles, or edible pearls.
