In a medium bowl, whisk together all-purpose flour, cake flour, baking powder, baking soda, and salt, then set aside.

In a large bowl, cream softened butter and granulated sugar with an electric mixer until light and fluffy for 2-3 minutes.

Beat in eggs one at a time, then stir in vanilla extract and sour cream until just combined.

Gradually add the dry ingredients to the wet ingredients on low speed until just combined, being careful not to overmix.

Cover the dough with plastic wrap and refrigerate for 1 to 24 hours to make it easier to handle and prevent spreading.

Preheat the oven to 375°F (190°C) and line baking sheets with parchment paper or silicone mats.

Lightly flour a surface, divide the chilled dough in half, and roll out one half to 1/4 inch thickness; cut out shapes with a 2-3 inch round cookie cutter.

Place cookies 1 inch apart on prepared baking sheets and bake for 7-9 minutes until edges are lightly golden and tops are set but still pale.

Let cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely before frosting.

While cookies cool, cream softened butter in a medium bowl, then gradually beat in sifted powdered sugar and milk until smooth and spreadable; add vanilla extract and food coloring if desired.

Once cookies are completely cool, spread a generous layer of frosting on each cookie and immediately top with sprinkles before the frosting sets.