Cut a piece of wax paper to fit the bottom of a 10" tube or bundt pan. In a large bowl, combine flour. salt, and poppy seeds. in another bowl, combine butter and 1 cup sugar, beat until light. Add egg yolks and beat well. mix in baking soda, sour cream and vanilla alternately with the flour and poppy seeds. Beat egg whites tyill stiff, mix in the remaining sugar. Fold white mixture into batter. pour batter into pan. Bake 250 for 1 hour or more.