Preheat oven to 350°F (180°C). Lightly grease a 9'' round cake pan.
Melt the butter in a medium saucepan over medium heat. Add brown sugar and whisk constantly until smooth (about 1 minute).
Pour the mixture into the prepared pan and arrange the sliced pears in a circle. Set aside.
Whisk almond flour, buckwheat flour, corn starch, baking powder, ground cinnamon, and salt in a large bowl.
In a medium bowl beat with a mixer the eggs, sugar, oil, and vanilla extract until well incorporated. Pour the mixture into the dry ingredients.
Beat until integrate everything, and the mixture is homogeneous (1 minute).
Pour the mixture into the prepared pan over the pears.
Cook for 40 minutes. To know if it´s ready insert a toothpick in the center and when it comes out it should be clean without a trace of batter.
Let cool for 15 minutes and remove from the pan.