
Preheat oven to 325°F (163°C). Spray bundt pan with gluten-free cooking spray.
In a large bowl, cream butter and sugar together with your mixer.
Add one egg at a time and combine. Once all eggs are incorporated, mix in the vanilla extract and buttermilk. Then, add the gluten-free all-purpose flour, gluten-free baking powder, baking soda, and ground cinnamon to your bowl and mix until fully combined. The batter will be very thick.
Peel and chop the apples into small pieces.
Stir in the chopped apples and chopped pecans and fold into the cake batter with a spoon or spatula.
Pour the batter into the greased bundt pan and bake for 70 minutes until a toothpick entered into the center comes out clean.
Combine butter, brown sugar, water, vanilla extract, and ground cinnamon in a small saucepan over medium-low heat. Stir continuously until the butter is melted and the sugar is dissolved. Do not bring it to a boil.
Poke holes all over the warm cake with a knife and pour the butter glaze evenly over the cake while still in the pan.
Allow the cake to cool completely in the pan and then invert the cake onto a serving plate. I sprinkled it with powdered sugar. Enjoy!