At least 1 day or up to 1 month in advance, make the vanilla sugar: Put the vanilla bean in a jar and pour the superfine sugar over it. Cover tightly and let set at room temperature overnight or for up to a month to infuse vanilla flavor into the sugar.
When ready to make the strawberries, place the vanilla sugar in a bowl. Whisk the egg whites with the lemon juice in another bowl until frothy. Holding the berries by their green tops, dip them in the egg whites 1 at a time, just up to their shoulders. Let the excess egg white drip off. Roll in the vanilla sugar to coat evenly and transfer to a cookie sheet, resting the berries point side up. Let set at room temperature until dry to the touch and serve the same day.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.