Cream together the unsalted butter and packed brown sugar in a stand mixer bowl using the paddle attachment on medium speed for about 2 minutes.

Add the egg and molasses to the butter-sugar mixture, mixing until well incorporated. Scrape down the sides of the bowl as needed.

Incorporate the pumpkin pie spice, ground ginger, black pepper, kosher salt, and baking soda into the mixture, and mix until combined.

Gradually add the all-purpose flour, mixing slowly at first to allow it to absorb, then increase speed until a smooth dough forms.

Lay the dough on plastic wrap, flatten it into a disc about one inch thick, wrap tightly, and refrigerate for at least 2 hours or overnight.

Preheat your oven to 325°F (160°C) and line a baking sheet with a silicone mat or parchment paper.

On a floured surface, roll out half of the chilled dough to about 1/4 inch thick and cut out tree shapes using a cookie cutter.

Transfer each cookie to the prepared baking sheet, leaving at least one inch of space between them.

Press M&M candies into the top of each cookie.

Bake for about 8 to 10 minutes, until the edges are dry and the centers are still soft.

Let the cookies cool on the baking sheet for approximately 10 minutes before transferring to a cooling rack.