Preheat the oven to 375°F (190°C). Place jumbo paper liners into the six wells of a jumbo muffin pan to prevent sticking and simplify removal after baking.

In a large mixing bowl, thoroughly whisk together the all-purpose flour, granulated sugar, packed dark brown sugar, salt, baking soda, pumpkin pie spice, nutmeg, and 1 teaspoon of ground cinnamon. Continue whisking until the mixture is uniform and free of visible lumps.

Add the eggs, pumpkin purée, vanilla extract, and vegetable oil directly to the dry mixture.

Using a spoon, gently stir the ingredients only until the batter comes together and no dry streaks of flour remain. Do not continue mixing beyond this point, as excessive stirring may produce dense muffins.

Divide the prepared batter evenly among the six lined muffin wells, filling each cavity nearly to the top.

In a small bowl, blend the 3 tablespoons of granulated sugar with the remaining 1 teaspoon of cinnamon. Distribute this cinnamon-sugar mixture evenly over the surface of each portion of batter.

Bake in the preheated oven for 25–30 minutes. At the 25-minute point, insert a toothpick into the center of one muffin. The muffins are finished when the toothpick emerges clean.

When necessary, continue baking for several additional minutes, checking frequently to prevent overbaking.

Leave the muffins in the pan for several minutes after removing them from the oven. Transfer them to a wire cooling rack and allow them to cool completely before serving.