In small heavy saucepan, combine blueberries, the sugar and lemon juice.
Bring to boil over high heat, stirring until sugar melts. Reduce heat to
medium; simmer 10 minutes or until thickened and reduced. Let cool. Pour
into a greased 9 inch springform pan.
In a large bowl, combine the flour through baking soda. Beat the egg,
lemon juice, butter and vanilla until mixed; stir into dry ingredients
until well combined. Fold in the lemon zest. Pour on top of the
blueberries in the springform pan.
Beat the cream cheese and sugar in a small bowl until smooth. Stir in
the egg and vanilla, mix well. Spread over batter and swirl with a
knife. Sprinkle remaining 1/2 c blueberries on top.
Place pan on a baking sheet. Bake at 350 degrees F for 45-55 minutes or
until golden brown and set. Cool on a wire rack for 15 minutes before
removing from pan.