In a large bowl, whisk together flour, sugar, baking powder, and salt. Set aside.
In a medium bowl whisk together the egg, buttermilk, sour cream, oil and vanilla.
Add the wet mixture to the dry, folding with a spatula until just the mixtures are combined. Do not overmix, it is ok to leave some small lumps in the batter.
Scrape the batter into the pan over the fruit. Be careful not to mess up your arrangement.
If you want, tuck the extra half pineapple rings into the sides of the pan. Place the round side down a few inches apart. This gets just a bit more pineapple in the cake and makes the sides quite pretty.
Bake for 38-40 minutes. The cake is done when the center is set and a toothpick inserted 1” into the center of the cake comes out with a few moist crumbs but no batter.
Place the pan on a wire rack to cool and set up for at least 30 minutes and up to overnight. If you plan to leave it overnight place a sheet of foil loosely over the top to keep the moisture in.
Run a thin spatula along the edges of the cake pan to make sure the cake is loose from the sides. Carefully invert it onto a serving platter and serve. This cake is good by itself or paired with a dollop of whipped cream or a scoop of vanilla ice cream. Store leftovers at room temperature for up to 3 days.