Preheat the oven to 350°F (175°C) and grease two 9-inch cake pans.
In a mixing bowl, whisk together the flour, baking powder, and salt.
In another bowl, beat the softened butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Gradually add the dry ingredients and milk alternately, mixing until just combined.
Divide the batter evenly between the prepared cake pans and smooth the tops.
Bake for 28-30 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for 10 minutes before transferring to a wire rack to cool completely.
Frost the cooled cakes with white buttercream frosting, smoothing the top and sides.
Roll out the black fondant and cut out Hello Kitty’s eyes and whiskers. Place them on the frosted cake.
Roll out the yellow fondant and cut a small oval for Hello Kitty’s nose. Place it below the eyes.
Roll out the pink fondant and shape it into Hello Kitty’s bow. Position it on the upper left side of the cake.
Chill the cake for 20 minutes before slicing and serving.