In a medium saucepan, combine berries, and 1 tablespoon water. Cook over medium-low heat until the berries "pop," stirring occasionally. Combine the 1-1/2 cups sugar, the flour, and nutmeg; add to the gooseberries in the saucepan. Cook and stir until mixture just begins to bubble. Spread mixture in the pastry-lined pie plate.
Preheat the oven to 400 degrees F (200 degrees C). Place a baking sheet on a lower oven rack. Stem and rinse gooseberries. Crush 1/2 cup berries in the bottom of a saucepan. Mix sugar, tapioca, and salt together in a small bowl; pour over crushed berries and mix until combined. Turn the heat to medium; cook and stir until mixture boils.
Preheat oven to 400 degrees F (200 degrees C). Place a baking sheet on a lower oven rack. Stem and rinse berries. Crush 1/2 cup berries in the bottom of a saucepan. Combine sugar, tapioca, and salt; mix with crushed berries. Pour fruit filling into pastry. Adjust top crust; cut slits to allow steam to escape.
In a medium bowl, stir together the flour and salt. Mix in the sour cream, eggs and vanilla. Add the gooseberry and sugar mixture, and stir to coat evenly.