Preheat the oven to 375 F. Line a standard sized muffin pan with 12 paper liners, and lightly spray the liners with non-stick baking spray.
In a saucepan, combine the oats, raisins, brown sugar, salt, cinnamon, nutmeg and milk. Cook the oatmeal over medium heat, stirring frequently, for about 5-6 minutes, until the oatmeal thickens to a creamy texture. Remove from the heat.
Stir the butter into the hot oatmeal until it's melted. Spread the oatmeal out onto a plate, and let cool for 10 minutes.
In a bowl, use a fork to whisk the oatmeal together with the eggs and vanilla.
Separately, combine the flour with the baking powder and baking soda. Add the flour mixture to the oatmeal mixture, and stir together briefly, just until moistened.
Divide the batter between the muffin cups, filling them nearly full. Sprinkle the Turbinado sugar over the muffin batter.
Bake the muffins on the center oven rack for about 15 minutes, until a toothpick comes out clean.
Cool the muffins for 2 minutes in the pan, then transfer the muffins to a cooling rack. Cool for 5 minutes, then serve warm with soft butter.