Preheat the oven to 350°F.
In a small bowl, stir together the flour, ginger, cinnamon, allspice and salt. In a large bowl beat together the butter, oil, and sugar until pale yellow and fluffy. Beat in the molasses and eggs until smooth. Put the baking soda into a small bowl or liquid (you’ll need extra room – it bubbles up) measuring cup, and add 3/4 cup boiling water.
Add a third of the dry ingredients to the butter-sugar mixture, beating on low speed just until blended. Add half the water mixture in the same way, then another third of the dry ingredients, the rest of the water mixture and the rest of the dry ingredients, blending just until combined. Fill paper-lined muffin tins 3/4 full and bake for 25 minutes, or until tops are springy to the touch.