In large bowl, sift or stir together flour, baking soda, baking powder, cinnamon, ginger, nutmeg, allspice, cloves, salt and pepper until evenly combined.
In bowl of mixer, cream together butter and sugar until light and fluffy, about 5 minutes. Add egg, molasses, lemon zest and rum and stir until evenly combined. Stir in flour and mix until just incorporated. Divide dough in two and form into disc. Wrap each in plastic wrap and place in fridge for at least 3 hours, or overnight.
Preheat oven to 350°F and line 2 baking sheets with parchment paper, set aside.
On lightly floured work surface, roll out dough one disc at a time into large circle about half an inch thick. Cut out 3-inch circles and place on prepared baking sheets. Bake until edges are light golden brown, about 10 to 12 minutes. Let cool on baking sheets for about 5 minutes, then transfer to wire rack to cool completely. Repeat with remaining dough until all cookies have been baked.
Once cookies have cooled completely, melt white chocolate in microwave or in a bowl set over simmering water. Dip cookies halfway in melted chocolate, return to baking sheet and garnish with sprinkles, if desired. Let chocolate set completely before serving. Cookies will keep for up to 4 days in refrigerator.