In a bowl, mix together the egg yolk and granulated sugar. Melt butter in milk and add to the bowl with the vanilla oil. Mix.
In a separate bowl, whip the egg white until it becomes like a stiff paste and forms a meringue. Mix in the flour and baking powder. Gently add in the mixture from Step 1 and cook in a waffle maker.
Make the custard. In a bowl, mix together the egg yolk and granulated sugar until it becomes white. Sift in the flour and mix well.
Heat milk and vanilla beans in a pot. Before it comes to a boil, turn off the heat and add the mixture from Step 3 in several batches. Mix well.
Heat Step 4 on medium heat, stirring constantly. When the edge of the mixture begins to bubble, use a whisk to smooth it out and remove from heat.
Pour Step 4 into a shallow container greased with butter and add butter on top as well. Tightly wrap with plastic wrap and cool.
Put the custard into the waffle, cut into 2 or 3 parts and it's ready. You can also wrap it decoratively to give as a gift.
If you want a chocolate waffle, in Step 2 add 1 tablespoon of cocoa powder to the batter and mix in. Another version can be found here (Recipe ID: 1991136).
Story Behind this Recipe
Since I got a waffle maker, I've been thinking of various different recipes.
Please preheat the waffle maker.
Make the custard on the stiffer side.
Try adding fruit and heavy cream for a smooth taste... green tea custard or chocolate custard is also delicious.
If you let these sit for more than a day, they'll become more moist.