For the Topping

1. Combine the oats, flour, brown sugar, pecans, cinnamon, and salt in medium bowl. Drizzle the melted butter over top and stir to combine. The mixture will be clumpy. Set aside.

For the Muffins

1. Line a 12-cup muffin tin with paper liners (or grease with a nonstick baking spray with flour in it).
2. Melt 2 tablespoons of the butter in 10-inch skillet over medium heat. Add the oats and cook, stirring frequently, until the oats turn golden and fragrant, 6 to 8 minutes. Transfer the oats to a food processor fitted with the metal blade and process into a fine meal. Add the flour, salt, cinnamon, baking powder, and baking soda to the oats and pulse until the mixture is uniform.
3. Melt the remaining 6 tablespoons of butter. In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Add the milk and eggs and whisk until the mixture is smooth (if you have lumps, I find it helpful to warm the mixture a bit in the microwave.) Gradually add the flour/oat mixture to the wet ingredients, stirring gently with the whisk until the dry ingredients are evenly moistened. Do not over-mix; the batter will look a little lumpy -- that's okay. You will notice that the batter is very thin; let it sit for 20 minutes to thicken (don't worry -- it will thicken quite a bit). Meanwhile, adjust an oven rack to the middle position and preheat the oven to 375°F.
4. Using an ice cream scoop with a wire scraper or large spoon, divide the batter equally into the muffin cups; they will be filled to the rim. Evenly sprinkle the streusel topping over the batter. Bake until golden and domed, and a toothpick inserted into the center of a muffin comes out clean, 22 to 25 minutes. (If your oven has hot spots, rotate the muffin tin halfway through baking.)
5. Let the muffins cool in the pan on a wire rack for 10 minutes. Remove the muffins from the pan and transfer to a wire rack to continue cooling. Serve warm or after they are completely cooled, store in an airtight container.
6. Freezer-Friendly Instructions: The muffins can be frozen in an airtight container or sealable plastic bag for up to 3 months. Thaw for 3 – 4 hours on the countertop before serving. To reheat, wrap individual muffins in aluminum foil and place in a preheated 350°F oven until warm.