- Put the first quantity of milk, sugar, butter and salt in a saucepan and heat.
- Cut the vanilla bean lengthwise, scrape the seeds and add to the saucepan.
- When the butter is completely melted, add the cocoa mass and mix until it is melted.
- Add the flour and whisk well just until the flour is incorporated.
- Use the spatula to scrape the sides of the dough and press down on it. When the dough separates from the sides of the pan, it's ready.
- Put the dough in the mixer bowl, add the second quantity of milk immediately and mix to cool down the temperature.
- Mix the eggs and the egg yolks together in a small bowl.
- Add half the eggs to the mixer bowl and mix on medium speed until well incorporated.
- Add the rest of the eggs little by little and mix well after each addition.
- Add the baking powder and rum and mix again on medium speed.
- Pour the dough into a food processor and turn it on.
- In the meantime, place the egg whites in the bowl of a tabletop mixer with a whisk attachment and mix on medium speed.
- Mix the second quantity of sugar and the dry egg whites in a bowl.
- After one or two minutes of whipping, add half the dry egg and sugar mix to the whipped egg whites. Add the rest
- Pour the dough into a mixing bowl.
- Add a little of the egg whites to the chocolate mix and mix to lighten it. Add the rest of the whipped whites and fold gently until well mixed.
- Adjust your raplette height to 0.4 cm (0.16").
- Place the silpat on the work surface.
- Place the raplette on the short side of the silpat, pour the dough mix in the raplette and swipe. Alternatively, if you don't have a raplette, you can spread the dough on the silpat with an offset spatula.
- Place the silpat on a metal tray and bake in a preheated 190° C (375°F) oven for 5 minutes.
- Let it cool completely and then place in a blast freezer until frozen.
- Flip the sheet of sponge cake on a parchment paper and then carefully peel the silpat away.
- With a ruler, measure the size of the silicone mold and cut rectangles in the sponge cake.
- Reserve until ready to use.