• Preheat oven to 350°F. Grease well a bundt pan with cooking spray. In a medium-sized bowl, add the flour, baking powder, baking soda, salt, and cinnamon and whisk to combine. Set aside.
• In the bowl of a stand mixer, or in a large bowl and an electric hand mixer, add the butter and granulated sugar. Cream together until smooth, add the vanilla and eggs one at a time, mix well. 
• Alternating between the sour cream and the dry mixture, add each a little at a time until fully mixed in. Scrape the sides down as needed. Add the grated apple and mix to combine. Set aside.
• In a small bowl, make the filling by mixing together the brown sugar, cinnamon, and pecans. 
• Pour 1/3 of the cake batter into the bundt pan and smooth out the top with a spatula. Sprinkle 1/2 of the filling on top evenly. Pour another 1/3 of the cake batter on top, and smooth. Add the remaining filling evenly. Top with the last of the batter and smooth the top. Bake for 60 minutes, until a toothpick inserted into the center, comes out mostly clean. A few crumbs are okay, but any wet batter means it needs to bake longer. 
• Let cake cool in the pan for 20 minutes, flip out onto a serving platter and let cool completely. 

For the glaze

• While the cake is cooling, make the glaze by whisking the melted butter and sugar together in a medium-sized bowl. Add the milk and vanilla, whisk until smooth.
• Pour the glaze over the top of the cooled cake, garnish with more pecans if desired.