Soak the gelatin. Peel the oranges (including the white skin) and cut out the fillets between the dividers. Drain, divide into 4 glasses, chill! Mix the blood orange juice with the sugar and heat gently. Dissolve the squeezed gelatine in it and let it cool down a little. Then fill up with the prosecco and pour into the glasses with the orange fillets. Cover with foil and leave to set in the refrigerator for at least 4 hours.
Before serving, stir the cream yogurt with vanilla sugar and lemon juice until smooth and distribute it between the glasses! If necessary, decorate with a stem of mint.