Preheat the oven to 350 degrees F. Grease a 9-inch square baking pan.
In the bowl of an electric mixer fitted with the paddle attachment, beat the butter and 1 cup of the sugar for 3 to 5 minutes on medium-high speed, until light and fluffy. With the mixer on low, add the eggs, one at a time, then the sour cream and vanilla, and mix until the batter is smooth. In a separate bowl, sift together the flour, baking soda, baking powder, and salt. With the mixer on low, slowly add the dry ingredients to the batter and mix just until combined. In a small bowl, combine the remaining 1/2 cup sugar and the cinnamon.
Spread half of the batter evenly in the pan. Top with half of the peaches, then sprinkle with two-thirds of the sugar mixture. Spread the remaining batter on top, arrange the remaining peaches on top, and sprinkle with the remaining sugar mixture and the pecans.
Bake the cake for 45 to 55 minutes, until a toothpick inserted in the center comes out clean. Serve warm or at room temperature.
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