Mix the flour, salt, sugar and baking powder in a bowl. Combine the beer and egg yolk, whisk into the flour, cover and leave to stand at room temperature for approx. 30 mins.
Carefully pit the plums so that they retain their shape. Insert 1 tsp of almond paste into the opening, press together gently.
Just before frying, beat the egg white with the salt until stiff. Add the sugar and continue to beat briefly, carefully fold the egg white into the beer batter. Heat the oil to approx. 180°C. Dip the plums in the batter in batches, drain and fry for approx. 3 mins. until golden brown, turning occasionally. Remove with a slotted spoon and drain on paper towels, serve warm.