Whisk dry ingredients:

In a large bowl, combine the flour, sugar, nutmeg, baking powder, baking soda, and salt by whisking.

Mix wet ingredients:

In a medium bowl, whisk the melted butter, oil, eggs, sour cream, and vanilla until homogeneous, then incorporate the buttermilk with a whisk.

Combine and rest batter:

Add the wet mixture to the dry ingredients and stir until just combined. Wrap the bowl with plastic film and allow it to rest at room temperature for 1 hour so the batter aerates, leading to taller muffins.

Preheat and grease pan:

When about 50 minutes have passed, heat the oven to 425°F (220°C) and grease the interior and top rims of a muffin pan to yield 10 muffins.

Fill muffin cups:

Employ a large scoop (e.g., an ice cream scoop) to gently deposit generous mounds of batter into the 10 cups, taking care not to deflate the airy texture.

Bake at two temperatures:

Bake for 8 minutes, then lower the oven setting to 350°F (175°C) and continue baking for an additional 6-8 minutes (there's no need to wait for the temperature to adjust).

Cool in pan:

Let the muffins rest in the pan for about 5 minutes, then carefully extract them and transfer to a wire rack.

Create inner cavity:

Using a skewer or chopstick, pierce a hole into the top of each muffin and gently rotate to form an inner cavity.

Roll in powdered sugar:

Put 2 cups of powdered sugar into a bowl. Roll the warm muffins one by one in the sugar to cover the entire exterior.

Inject raspberry jam:

Attach a narrow tip suitable for jam to a piping bag. Fill the bag with raspberry jam and inject each muffin until the jam begins to emerge from the hole.

Enjoy immediately:

Cut one open and savor! Best consumed immediately, akin to a donut.