Combine flours, sugar, and salt. Cut in butter or shortening with pastry blender until particles are pea-size.
Combine lemon juice, milk, and egg yolk. Sprinkle over flour mixture, toss with fork until all flour is moistened and dough forms. Gather dough in ball. Press (or roll) dough into 12-inch tart shell. (Pie pan or individual tart shells can be substituted). Prick bottom and sides of pastry with fork; chill.
Brush with lightly beaten egg white. Bake at 475° for 12-14 minutes or until lightly browned. Cool before filling.
In wide pan or skillet, bring 1 cup water, sugar, and lemon juice to boil.
Peel, core, and halve pears. Place halves cut side down in single layer in boiling liquid. Spoon liquid over pears, cover, reduce heat, and simmer 5-8 minutes or until pears are poached but firm.
Remove pears; drain on paper towels. Combine cornstarch with 1 tbsp. water. Add to poaching liquid. Bring to boil, cooking until thickened and clear, stirring constantly; cool.
Whip cream cheese and add thickened pear syrup. Spread on bottom of baked tart shell. Arrange pears cut side down over filling.
Melt chocolate and butter in small saucepan (or microwave), stirring until smooth. Drizzle over pears. Chill.