Preheat oven to 350° F. Line bottom and sides of 14-inch square pan or 11 x 17-inch baking pan with parchment paper. Cream together butter and sugar until smooth. Beat in extracts. Add egg and salt, beating until smooth. Gradually stir in ground almonds and flour to form a dough. Press crust into bottom of baking pan and chill while preparing filling.
For filling, cream together butter and sugar until fluffy. Add eggs, 1 at a time, beating well after each addition. Blend in extracts, ground almonds, flour and brandy until just combined. Spread filling mixture evenly over pastry in pan. Arrange plum halves, flat side down, in neat rows over filling (do not overcrowd). Bake for 40 to 45 minutes, until filling rises around plums a bit and sets. Allow to cool.
Warm apricot jam in microwave or over low heat in a saucepot and brush onto surface of tart or dust with icing sugar.
Tart is best served at room temperature but can be stored refrigerated for up to 3 days.
Yield: 1 14-inch square pan or 11 x 17-inch baking pan. Makes 24 servings.