• Preheat oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper, making sure there is an overhang on the sides to help lift the cake out later.

For The Sponge Cake

• In a bowl, whisk together the flour, baking powder, and salt.
• In a large mixing bowl, beat the egg yolks with 1/2 cup sugar until pale and thick. Stir in the milk and vanilla.
• In a separate bowl, beat the egg whites until foamy, then gradually add the remaining 1/2 cup sugar, beating until stiff peaks form.
• Gently fold the egg whites into the yolk mixture, then fold in the dry ingredients.
• Pour the batter into the prepared baking dish and bake for 20-25 minutes, until golden and a toothpick inserted in the center comes out clean. Let cool completely.
• Carefully lift the cooled cake out of the baking dish using the parchment paper overhang.
• If the cake feels too soft or fragile to cut without breaking, you can skip slicing it in half and leave it as one full layer. This keeps things simple, and you can just spread the mascarpone mixture right on top later.
• If the cake is firm enough to handle, slice it in half horizontally to create two layers. Place both layers back into the original baking dish so they fit properly.

For The Tres Leches Soak

• In a bowl, whisk together the condensed milk, evaporated milk, heavy cream, and coffee.
• Poke holes all over both layers with a fork. Slowly pour the entire tres leches mixture over the cake, guiding the liquid into the holes using a spoon or spatula.
• Refrigerate for at least 2 hours to allow the cake to fully soak up the liquid.

Assembly

• When ready to assemble, make the mascarpone cream.
• In a bowl, beat the mascarpone, powdered sugar, and vanilla until smooth.
• In a separate bowl, whip the heavy cream until stiff peaks form. Fold the whipped cream into the mascarpone mixture until smooth and fluffy.
• If you kept the cake as one full layer, simply spread the mascarpone mixture evenly over the top, dust with cocoa powder, and refrigerate. Otherwise, continue with the layering steps.
• Carefully remove the soaked cake from the baking dish using the parchment paper overhang and place it onto a sheet pan or cookie sheet.
• Place a serving platter or serving dish ( I used another 9x13 Sheet Pan lined with parchment) over the cake, then carefully flip the whole cake so that the top becomes the bottom.
• Carefully remove the now top layer and set it aside. If it's too wet or delicate, slide a chopping board underneath to help lift and transfer it.
• Spread half of the mascarpone mixture evenly over the bottom cake layer.
• Gently place the top cake layer back on. If needed, use a chopping board to support it before transferring it back.
• Spread the remaining mascarpone cream evenly over the top.
• Dust with cocoa powder using a fine sieve.
• Refrigerate for at least 2 hours (or overnight) before serving to allow the flavors to meld.