Peel, core and slice apples about 1/4 inch thick. Place in a mixture of water and lemon juice to prevent browning. Set aside.
Preheat oven to 450°F.
Toast pecans on ungreased baking sheet in oven until lightly browned, about 10 minutes. Check frequently to prevent burning.
Reduce oven temperature to 325°F.
Melt butter in small, heavy saucepan. Add brown sugar and cook, stirring, just until melted, 3 to 5 minutes. Watch closely because sugar burns easily.
Pour butter-sugar mixture into 9 inch round nonstick cake pan and spread to coat bottom. Sprinkle chopped pecans on top butter-sugar mixture. Drain and pat dry apples and place in circles, slightly overlapping, over pecans.
Sift flour, baking powder, cinnamon and salt into bowl. Using electric mixer, beat butter at medium speed until light and fluffy. Add sugar and continue beating until creamy, 3 to 5 minutes. Add egg and vanilla and continue beating until completely incorporated.
Reduce speed to low, add flour mixture and milk, alternating, in 3 additions. Continue to mix only until dry ingredients are completely mixed in, stopping to scrape sides if necessary.
Spoon batter over topping and spread carefully so batter is even.
Bake 55 minutes, or until tester comes out clean. Cool in pan 10 to 15 minutes. Carefully run spatula around edge of pan and let stand another 10 to 15 minutes.
Invert pan over large plate and let stand 3 minutes. Carefully remove pan.