Preheat oven to 350°F (175°C).

Prepare a cupcake pan with liners.

In a medium bowl, cream together sugar and butter until light and fluffy (about 2 minutes).

Beat in egg yolks for another minute.

In a separate small bowl, beat egg whites until soft peaks form.

In another bowl, sift together flour, baking powder, salt, and cinnamon.

In a separate bowl, whisk together horchata and vanilla.

Gradually add dry ingredients and wet ingredients to the creamed mixture, alternating between the two, beginning and ending with the dry ingredients.

Beat well after each addition.

Gently fold in the beaten egg whites until just incorporated.

Fill each cupcake liner 2/3 full.

Bake for 20 minutes, or until a cake tester inserted into the center comes out clean.

Let cupcakes cool completely on a wire rack.

For the frosting, whip the cream together with the confectioner's sugar in a cold metal bowl until it thickens.

Add horchata, vanilla, nutmeg, and cinnamon to the whipped cream.

Mix until well combined.

Frost the cooled cupcakes with the horchata frosting.