Preheat the oven to 180°C (approximately 350°F). Grease the ramekins.
Bring 1/2 of the milk, the vanilla bean seeds, vanilla bean pod, salt and butter to a boil. Mix the remaining milk with the flour until smooth, stir into the boiling milk and simmer for 5 minutes, stirring. Remove the vanilla bean pod and let cool slightly. Stir in 1 egg.
Separate the remaining eggs. Whip the egg whites until stiff and chill.
Whisk the egg yolks with the sugar until light and fluffy. Add the finely grated lemon zest, the lemon juice and the rum.
Fold in the almonds and egg whites. Distribute between the ramekins and bake until golden, about 20 minutes. Dust with powdered sugar and serve immediately.