Preheat your oven to 325°F (163°C) and prepare a 9x5 inch loaf pan by greasing it thoroughly and lining with parchment paper.

In a medium bowl, whisk together the all-purpose flour, cake flour, baking powder, and salt.

In a stand mixer, cream the room-temperature butter and granulated sugar until light and fluffy, about 4 minutes.

Add eggs one at a time, mixing well after each addition, then stir in vanilla.

Gradually add the flour mixture to the wet ingredients, alternating with milk and yogurt, mixing gently until just combined.

Fold in the rainbow sprinkles gently.

Pour the batter into the prepared loaf pan and bake for 60-65 minutes, checking for doneness after 50 minutes.

Remove from the oven, let cool in the pan for 10 minutes, then transfer to a wire rack.

In a mixing bowl, whisk together the sifted confectioner's sugar, heavy cream, and Greek yogurt until smooth.

Once cooled, glaze the cake and allow it to drizzle down the sides.