Preheat the oven to 350°F. Lightly coat 24 standard muffin cups with nonstick cooking spray and set the prepared pans aside.

Place the cooled melted butter, pumpkin purée, room-temperature eggs, granulated sugar, and vanilla extract in a large mixing bowl. Whisk until the ingredients form a smooth, evenly blended mixture.

In a separate bowl, thoroughly combine the einkorn flour, baking soda, baking powder, cinnamon, nutmeg, ginger, and salt. Stir well so the leavening agents and spices are distributed uniformly.

Pour the pumpkin mixture into the bowl of dry ingredients. Fold gently only until no large streaks of dry flour remain. Avoid excessive mixing, which can negatively affect the finished texture.

Cover the bowl with plastic wrap and leave the batter to rest for at least 20 minutes. For advance preparation, the covered batter may be refrigerated overnight. This resting period allows the einkorn flour to absorb the liquid and contributes to a more delicate, consistent crumb.

While the batter rests, process the rolled oats in a blender or food processor until they reach a fine, cornmeal-like texture. Transfer the ground oats to a small bowl and mix them thoroughly with the packed brown sugar, einkorn flour, and cinnamon.

After resting, stir the muffin batter briefly to eliminate any remaining dry pockets or uneven areas.

Distribute the batter among the prepared muffin cups, filling each cavity approximately three-quarters full. Use roughly ¼ cup of batter for each muffin.

Scatter approximately ¾ tablespoon of the oat streusel evenly over the top of each portion of batter.

Bake for 25–30 minutes. The muffins are ready when a toothpick inserted into the center emerges clean or with only a few moist crumbs attached.

Let the muffins remain in the pans for several minutes before transferring them to a wire cooling rack. Serve warm or allow them to cool completely.