1. Preheat oven to 350°F and line 2 large rimmed baking sheets with parchment. In a medium bowl, whisk together flour, baking soda, salt, cinnamon, ginger, nutmeg, cloves and pepper until well combined. Stir buttermilk and vanilla in a small bowl.
2. In a large bowl, using an electric mixer on medium-high speed, beat butter and brown sugar until light and fluffy, about 3 minutes. Add egg and molasses, beating until well combined. Reduce speed to low and beat in half of flour mixture until just combined. Beat in buttermilk mixture, then remaining flour mixture, beating until smooth. Using a small ice cream scoop or a couple of tablespoons, drop 2-tablespoonful-size mounds of batter at least 2 inches apart on baking sheets. Bake for 11 to 13 minutes, switching baking sheets from top to bottom halfway through, until cookies are puffed and spring back when lightly touched. Let cool on sheets on a wire rack for 5 minutes, then transfer cookies to racks to cool completely.
3. Make filling: In a large bowl, using an electric mixer on medium speed, beat all ingredients together until smooth, about 3 minutes. Chill bowl in refrigerator 15 minutes.
4. Spread about 2 tsp. filling on flat side of half of cookies. Press flat sides of remaining cookies onto filling.