Put sugar and yolks in a large bowl, and beat with a mixer at high speed until pale yellow. Gradually add flour, beating until smooth.
Heat milk over medium-high heat in a medium, heavy saucepan to 180° or until tiny bubbles form around edge (do not boil). Gradually add the hot milk to sugar mixture, stirring constantly with a whisk. Return the milk mixture to pan. Cook the mixture over medium heat until thick (about 8 minutes), stirring constantly. Remove from heat. Stir in rind.
Spoon 1/4 cup custard into the bottom of a 2-quart soufflé dish or compote. Arrange one-third of the cake slices in a single layer over custard. Combine the grenadine, Drambuie, cognac, and rum. Brush the grenadine mixture over cake slices until wet. Spread 1 1/4 cups custard over cake slices. Arrange one-third of the cake slices in a single layer over custard. Brush the grenadine mixture over cake slices until wet. Combine 1 1/4 cups custard and chocolate, and spread over cake slices. Arrange remaining cake slices over custard. Brush with remaining grenadine mixture. Spread remaining custard over cake slices. Sprinkle with almonds. Cover and chill at least 4 hours.