For the lemon tartlets, soak the gelatine in cold water, squeeze out and dissolve in a little hot water.
Mix the ricotta with the cream, sugar, lemon juice and zest and the dissolved gelatine until well blended. Pour the cream into small metal rings 8 cm in diameter and 4 cm high and refrigerate for about 2 hours.
Blanch kumquats briefly in boiling salted water to lose the bitterness. Rinse, cut in half, remove seeds and simmer with orange juice, sugar and vanilla bean for about 5 minutes.
Stir cornstarch in a little water until smooth and mix into the ragout. Remove vanilla bean and let ragout cool. Peel the rings off the ricotta tartlets.
Arrange the lemon tartlets on dessert plates and garnish with the kumquat ragout and mint leaves.