In a large mixing bowl, whisk together the flour, salt, baking powder, baking soda and granulated sugar. Make a well in the center and set aside.
In a small mixing bowl lightly whisk the eggs. Add the buttermilk, 1/4 cup reserved pineapple juice, the melted cooled butter and vanilla. Whisk until blended.
Pour the buttermilk mixture into the flour mixture and gently fold together with a spatula until the flour is incorporated. The batter will be thick and lumpy, this is okay. Gently scoop dollops of batter into the prepared pan taking care not to move the pineapple rings. Gently smooth the top.
Place the cake pan on a foil lined baking sheet and bake at 350 degrees F until a toothpick comes out with no wet batter, about 45-50 minutes. Tent the cake with foil if over-browning. Allow the cake to cool in the pan for 15-20 minutes.
Invert a serving platter over the cake pan. Invert the cake pan and platter together, then lift off the cake pan. Cool to room temperature, slice and serve.