Wash the apple and cut into pieces. Steam in lemon juice and 3-5 tablespoons of water for about 5 minutes. Flavour with sweetener. Let cool off. Bring milk and salt to the boil. Remove the pot from the stove. Stir in semolina and possibly vanilla pulp.
Let it swell for 5-10 minutes. Separate egg. Stir egg yolk into the hot semolina. Beat egg white until stiff and fold in. Flavour semolina with sweetener. Serve semolina with apple compote. Sprinkle semolina with pistachios and garnish with mint if necessary.