Preheat the oven to 350° Fahrenheit (176° Celsius). Line an 8x8-inch square baking pan with parchment paper. Set aside.
In a medium bowl, whisk together dry ingredients (flour, baking powder, baking soda, cinnamon, nutmeg, ginger, cloves, and salt). Set aside.
In a large bowl, vigorously whisk melted butter, brown sugar, and white sugar. Add the egg, pumpkin puree, and vanilla extract. Whisk well until combined.
Sift the dry ingredients into the wet ingredients. Stir with a spatula until just combined, with no flour streaks. Gently fold in white chocolate chunks.
Pour the batter into the lined baking pan. Bake for 18-20 minutes, until the edges are lightly golden brown and a toothpick comes out clean. (The center will feel somewhat soft to the touch, but will firm up.)
Let cool, then slice into bars!