Cut vanilla bean lengthwise, scrape out the seeds and add pod and seeds to the milk in a saucepan. Add the sugar and cardamom and simmer for 10 minutes. Soak the gelatin in cold water. Remove the vanilla bean and cardamom pods from the milk. Sprinkle in the semolina while stirring and cook for 5 minutes.
Dissolve the soaked gelatin in a little hot water and mix it in with the semolina. Let the semolina mixture cool, stirring occasionally. Whip the heavy cream until stiff and fold into the semolina mixture. Pour into a 3/4 liter (approximately 3 1/2 cups) pudding mold and refrigerate for 5 hours.
Peel grapefruits, removing all of the white pith. Cut segments out of separating membranes. Heat honey in a saucepan and add grapefruit segments. Toast almonds in a dry pan. Dip pudding mold briefly in hot water, unmold and garnish with grapefruit segments, almonds and mint leaves.