Preheat the oven to 180C/350F/Gas 4. Line a 12-cup muffin tin with muffin cases, and set aside.
Whisk together the flour, baking powder, baking soda, salt, and spices. Set aside.
Whisk together the eggs. Add the sugar, and whisk until combined. Add the butter, yogurt, and molasses, and whisk until combined. Fold in the dry ingredients until smooth and combined.
Divide the batter evenly between the muffin cups, filling only 2/3 full. Bake for 15 - 17 minutes, or until a toothpick inserted into the centre comes out clean.
Allow to cool for 5 minutes in the pan, before transferring them to a wire rack to cool completely before frosting.
For the Frosting
Using a handheld or stand mixer, beat the butter until pale and creamy. Add half of the icing sugar, and beat until combined. Add the remaining sugar and beat until combined. Add the molasses, milk, and spices, and beat until light and fluffy.
Transfer the frosting to a piping bag, and frost the cooled cupcakes. Top with festive sprinkles!
Notes
*Make your own cake flour! Measure out 1 and 1/2 cups (187g) of plain/all-purpose flour, remove 3 tablespoons, and replace with 3 tablespoons of cornflour/cornstarch. Sift well.**Light or true molasses is much sweeter than blackstrap molasses (which is very bitter), and is much preferred in baking. Black treacle is also fine to use.Leftover cupcakes can be stored, covered tightly, in the fridge for up to 3 days. Frosted or unfrosted cupcakes can be frozen for up to 3 months. Thaw overnight in the fridge.Cupcakes can be made 1 day in advance, covered, and stored at room temperature. Cover the frosting, and store in the fridge until ready to use.