Preheat your oven to 350 degrees, and line a 14x11 inch baking sheet with parchment paper.

Using a stand mixer fitted with the whisk attachment, beat together 4 egg yolks, 1/3 cup of the sugar, and 1/4 cup of horchata on high speed for about 5 minutes until mixture becomes thick and doubles in size. Transfer the mixture to a large bowl and set aside. Clean and dry the mixing bowl and whisk attachment.

Place the egg whites in the mixing bowl and beat using the whisk attachment on medium speed for 2 minutes, until the whites start to froth. Slowly add the remaining 1/3 cup of sugar while gradually increasing the speed. Keep whipping until a stiff meringue forms, about 3-4 minutes.

Using a rubber spatula, gently fold your meringue mixture into the yolk mixture.

Sift the flour and pinch of salt over the top of your mixture and fold in gently. Spread the batter evenly in your prepared pan.

Bake for 14 minutes, or until top is golden brown and springs back when gently pressed down. Set aside to cool.

Once your cake has cooled, create a stencil of the bottom of your baking dish and use it to cut out the shape of your dish. You should have enough cake for two rounds.

Using an electric mixer on low speed, beat mascarpone, sugar, egg yolks, horchata, and salt in a large bowl. Gradually increase the speed to medium as mixture becomes fluffier. Beat until soft peaks form, making sure you don't over-whip.

Spread a thin layer of mascarpone cream in your serving dish. Place one of your sponge cake rounds on top, with the top of the cake facing down to ensure the the liquid is well absorbed.

Using a squirt bottle or spoon, soak cake with 1/3 cup of your horchata/coffee mixture. Spread half of the remaining mascarpone cream over it and place second cake half on top, and soak again with remaining horchata/coffee mixture.Top with the remaining marscapone cream.

Using a fine mesh sieve, dust the cocoa powder over your tiramisu, making sure every inch is covered.

Cover and store tiramisu in the fridge for 6-8 hours before serving.