For Sponge:
6 tablespoons warm water
1 teaspoon sugar
1 1/2 teaspoons dry active yeast
1/4 cup unbleached all-purpose flour

For Dough:
Sponge (see above)
6 tablespoons Greek yogurt
4 tablespoons unsalted butter, at room temperature
2 large eggs, divided
1/4 cup sugar
1 teaspoon salt
1 teaspoon vanilla extract
2 1/2 cups all purpose flour

For Filling:
1/3 cup cream cheese, softened
2 tablespoons Greek yogurt
2 tablespoons sugar
2 teaspoons fresh lemon juice
2 tablespoons flour
1 cup strawberry preserves