Preheat oven to 350°F (175°C) and grease your 9×13-inch pan.
Sift together flour, cocoa, baking powder, and salt.
In a large bowl, beat eggs and sugar until light and fluffy (5-6 minutes).
Gently fold in dry ingredients.
Stir in milk and vanilla until just combined.
Transfer the batter to the prepared pan and bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean.
Let the cake cool completely. Poke holes all over the surface.
Combine the sweetened condensed milk, evaporated milk, and heavy cream in a bowl and mix until well blended. Slowly pour over the cake.
Refrigerate for 4–6 hours or overnight.
Top with whipped cream and optional chocolate shavings.
