Preheat the oven to 350?F (175?C) and grease a baking pan.

In a mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.

Add the melted butter, eggs, vanilla extract, and milk to the dry ingredients and mix until smooth.

Pour the batter into the prepared baking pan and bake for 25-30 minutes, or until a toothpick comes out clean.

Let the cake cool completely in the pan.

In a bowl, combine the sweetened condensed milk, evaporated milk, whole milk, and vanilla extract.

Once the cake is cooled, poke holes all over the surface using a toothpick.

Pour the tres leches mixture evenly over the cake, allowing it to soak in.

In a mixing bowl, whip the heavy cream with powdered sugar and vanilla extract until soft peaks form.

Spread the whipped cream over the soaked cake and garnish with chocolate shavings.

Cut into bars and serve chilled.