In a large bowl, with a mixer on medium speed, beat 1/2 cup butter and the brown sugar until well blended. Add eggs and beat until smooth. In a small bowl, stir baking soda in 1 tablespoon hot water until dissolved; beat into butter mixture.
In a medium bowl, mix flour, cinnamon, nutmeg, cloves, ginger, and salt. Add to butter mixture, stir to mix, then beat until well blended. Stir in pecans and citron.
Divide dough in half and shape each portion into a log about 11 inches long and 1 1/2 inches in diameter. Wrap logs separately in waxed paper and freeze until firm enough to slice, at least 1 hour.
Unwrap dough. Cut logs crosswise into 1/4-inch-thick rounds and place about 1 inch apart on buttered 12- by 15-inch baking sheets.
Bake cookies in a 350° regular or convection oven until lightly browned, 8 to 12 minutes; if baking two sheets at once in one oven, switch their positions halfway through baking. Let cookies cool on sheets for 5 minutes, then use a wide spatula to transfer to racks to cool completely.
Nutritional analysis per cookie.