Preheat the oven to 180 degrees C. Butter or line with paper liners a 12-cup muffin tin.
Cream 5 tablespoons of the butter with the white sugar. Add the molasses and the egg and egg yolk.
Sift together the flour, cocoa powder, ginger, cinnamon, allspice, nutmeg and salt. Dissolve the bicarb soda in the hot milk. Add the flour mixture to the creamed mixture and stir until just combined. Stir in the hot milk mixture. Pour the batter evenly into the prepared tin.
Bake for 20 minutes or until slightly springy to the touch. Allow to cool a few minutes in the pan and remove to a rack to cool.
To make icing: Cream the 2 tablespoons butter and the cream cheese together. Beat in the icing sugar until fluffy. Add the lemon essence and beat. Ice when the cupcakes are cool.