Beat butter, cream cheese, sugar, salt and almond extract in medium-size bowl until light and fluffy, 3 minutes. Stir in flour until smooth. Stir in almonds. Shape dough into 10-inch long log with 1-1/2-inch diameter. Wrap in plastic wrap; refrigerate 2 hours or overnight.
To bake, heat oven to 350 degrees F.
Slice dough into 30 equal pieces. Press each piece in bottom and up side of ungreased 1-3/4 x 1-inch gem muffin-pan cup to form shell, for 30 shells.
Bake in 350 degree F oven 15 to 20 minutes, until lightly browned. Transfer pans to racks; cool slightly. Loosen shells with tip of paring knife; lift out to wire racks to cool completely.
When cool, combine white chocolate and shortening in small, heavy saucepan over low heat; heat, stirring occasionally, until melted and smooth. Let cool slightly.
Spoon 1/4 teaspoon chocolate mixture into bottom of each shell; let stand until firm, 10 minutes. Spoon about 3/4 teaspoon mint jelly into each, leaving about 1/8 inch space at top.
Pour thin layer of melted white chocolate over tops of half of the tarts. Drizzle or decorate remaining tarts with remaining white chocolate. When chocolate is almost set but slightly sticky, top with sprinkles, if desired. Refrigerate until ready to serve. Makes 2-1/2 dozen mini tarts.