Preheat oven to 400°F. Coat a 12-cup muffin pan with cooking spray, or line it with muffin papers. In medium bowl, whisk together the first six ingredients until well-mixed. In large bowl, whisk together brown sugar, molasses, oil, and one egg until combined. Add the other egg, pumpkin, and vanilla, and whisk again until combined. Gradually add flour mixture to wet ingredients, alternating with buttermilk, until just combined, being careful not over mix. Stir in 1/2 cup peanuts. Pour batter into prepared muffin pan, filling each one about 3/4 full. Sprinkle top of each muffin with remaining 1/4 cup chopped peanuts. Bake until puffed and golden brown and a toothpick inserted into the center of a muffin comes out clean, about 20 minutes. Cool muffins in the pan on a wire rack for 15 to 20 minutes. Slide a knife around edges of muffins to loosen them from pan if no paper was used. Serve warm or cool; store in an airtight container or resealable plastic bag for up to 4 days, or freeze for up to 4 months. Makes 12 muffins.