Preheat oven to 350°F. Line bottom and sides of a 9 x 9 inch square baking pan with parchment, leaving an overhang on all sides. In a medium bowl, whisk together flour, spices, baking soda, and salt and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream butter and sugars on medium-high speed until smooth, scraping down the sides as necessary. Beat in egg and vanilla until well combined. Beat in pumpkin puree. Reducing the speed to low, add the dry ingredients and mix until just combined. Fold in ¾ cup of the pecans.
Spread batter evenly in prepared pan. Sprinkle remaining ¼ cup of pecans on top. Bake until a toothpick inserted in center comes out with just a few moist crumbs attached, about 40 to 45 minutes. Cool completely in pan before cutting.