In a large bowl mix together melted butter with brown sugar and white sugar using a rubber or silicone spatula, until combined.
Add egg and molasses, continuing to mix until uniform consistency forms.
Add cinnamon, ginger, baking soda, and oat flour, ½ cup at a time, until well-incorporated.
Cover the bowl and refrigerate for at least one hour, up to overnight.
When ready to bake, preheat the oven to 350°F. Line a large baking sheet with parchment paper. Pour shimmer sugar (or large crystallized white sugar) into a small bowl.
Using an ice cream scoop, scoop the dough and roll into a smooth ball. Roll in the shimmer sugar. Place on the baking sheet, at least a few inches apart.
Bake for 11 minutes until the edges brown. Let cool completely on the baking sheet.
Store in an airtight container for 3-5 days. Freeze for up to 3 months.
