Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or grease it with cooking spray.

In a medium bowl, whisk together flour, baking powder, baking soda, ground ginger, ground cinnamon, ground nutmeg, and salt. Set aside.

In a large mixing bowl, beat together softened butter and dark brown sugar until light and fluffy, about 2-3 minutes.

Add eggs one at a time, mixing well after each; then add molasses and sour cream/yogurt until fully combined.

Gradually add dry ingredients to the wet mixture, mixing on low until just combined. Fold in optional nuts and crystallized ginger.

Divide the batter among the muffin tins, filling each cup about two-thirds full.

Bake for 18-22 minutes, until a toothpick inserted comes out clean or with a few moist crumbs.

Let the muffins cool in the pan for about 5 minutes before transferring to a cooling rack.

Whisk together powdered sugar and milk in a separate bowl until smooth for the glaze.

Drizzle the glaze over the cooled muffins and serve.