Preheat oven to 400°F. Remove puff pastry from freezer to defrost.
Peel, core and quarter apples and pears. Toss with lemon juice.
Cream together butter, sugar, ginger and salt. Spread mixture on bottom and sides of a 10-inch round thick-bottomed flameproof and ovenproof baking pan or skillet.
Place apple and pear wedges skinned side down in alternating concentric circles on top of butter mixture. (Cut any extra pieces to fill in gaps and pack tightly since tart will shrink when baked.)
Place pan over medium-high heat and cook fruit for about 20 minutes or until butter mixture begins to brown. Remove pan from heat; cool slightly.
On a floured surface, lightly roll out one sheet of puff pastry and cut out a 10-inch round using base of a 10-inch tart pan or a stencil. Using a fork, poke holes all over pastry. Place pastry on top of fruit in pan, tucking in outer edges to seal.
Bake tart until pastry turns golden, about 30 minutes.
Remove tart from oven and let cool for about 20 minutes. While pan is still warm, remove tart: Place a plate over top of pan and, holding plate firmly, invert pan quickly onto plate; remove pan. Serve warm with vanilla ice cream, if desired.