Preheat the oven to 350°F. Grease a 10 by 3-inch round pan with butter, line the bottom and sides of the pan with parchment paper, and grease the paper. (I’ll let you just grease, line the bottom of the pan, and lightly flour the sides if you’re feeling lazy.)
Place a large sifter or a sieve in a large mixing bowl. Add the flour, cocoa, baking powder, baking soda, and salt and sift.
Add the sugar and whisk until combined.
In another large bowl, whisk the eggs, milk, oil, and vanilla together.
Gradually add the wet ingredients to the dry ingredients and whisk until there are no lumps and the batter is smooth.
Carefully pour in the boiling water and stir until combined. (Watch the little ones with the hot water!)
Pour the batter into the prepared pan. Bake in the center of the oven for approximately 50 minutes or until a wooden skewer inserted in the center comes out clean, and the cake bounces back when lightly pressed.
Remove from the oven and let the cake stand for 10 minutes.
Reserve 3 tablespoons condensed milk in an airtight container in the fridge for later. In a large bowl, combine the evaporated milk, the rest of the condensed milk, and heavy cream. Add the vanilla bean seeds and whisk together.
While the cake is still in the pan, use a skewer to poke holes in the top of the cake. Spoon the milk mixture over the top of the cake, giving it time to gradually soak into the cake. Cover the cake with plastic wrap and refrigerate overnight or for at least 5 to 6 hours.
Make the condensed milk whipped cream: Pour the cream into a cold large metal bowl. Add the 3 tablespoons condensed milk. Using a balloon whisk, begin to whisk the cream until it has doubled in volume, has smooth soft peeks, and is light and fluffy.
Top the cooled cake with the condensed milk whipped cream. Sprinkle shaved semisweet chocolate on top.