Preheat oven to 375°F In medium bowl, combine sweetened condensed milk, sour cream, 4 tablespoons lemon juice and vanilla; mix well. Chill.
In large bowl, beat 1/2 cup butter and brown sugar until fluffy. Add flour and 3/4 cup nuts; mix well.
On lightly greased pizza pan or baking sheet, press dough into 12-inch circle, forming rim around edge. Prick with fork. Bake 10 to 12 minutes or until golden brown. Cool.
Arrange 2 sliced bananas on cooled crust. Spoon filling evenly over bananas. Dip remaining banana slices in remaining 2 tablespoons lemon juice; arrange on top along with pineapple, cherries and additional nuts.
In small saucepan, over low heat, melt chocolate with remaining 1 tablespoon butter; drizzle over pie. Chill thoroughly. Store leftovers covered in refrigerator.