Soften gelatin in boiling water; set aside.
Beat egg yolks in top of a double boiler. Add pumpkin, brown sugar, spices, and salt, mixing well. Cook over boiling water, stirring occasionally, until thoroughly heated. Add gelatin mixture, mixing well. Chill until mixture mounds when dropped from a spoon.
Beat egg whites (at room temperature) until foamy. Gradually add sugar, beating until stiff peaks form. Fold into pumpkin mixture. Spoon mixture evenly into tart shells. Chill until firm. Garnish with whipped cream, if desired.