Preheat your oven to 350 F. Melt 1/3 cup butter in a 10-inch cast iron skillet or oven-safe skillet over medium heat. Add the brown sugar and salt, stirring until the mixture bubbles and becomes smooth and caramel-like, about 2 to 3 minutes. Remove from heat.
Arrange the pear slices in a beautiful fan pattern over the caramel. Sprinkle with 1/2 teaspoon of cinnamon. Set aside while you make the batter.
Whisk together the almond flour, gluten free flour, baking powder, baking soda, salt, and cinnamon in a medium bowl.
In a large bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3 minutes. Add the eggs one at a time, beating well after each. Mix in the vanilla.
Add half the flour mixture and stir until just incorporated. Add the sour cream, stir to combine, then add the remaining flour mixture. Mix until you have a smooth, thick batter.
Carefully dollop the batter over the arranged pears and spread it evenly without disturbing the fruit underneath. Smooth the top with an offset spatula.
Bake for 40 to 48 minutes until the cake is golden and a toothpick inserted in the center comes out clean. Let the cake cool in the skillet for exactly 5 minutes.
Run a spatula around the edges, place a serving plate over the skillet, and flip in one swift motion. Let it sit for a moment before lifting the skillet away. Serve warm.