Line two half-sheet pans with parchment paper and set aside.
For the cookie dough
Place the soft butter in a medium-large mixing bowl and stir for 10-15 seconds until nice and creamy. 1 cup very soft butter
Add the powdered sugar and cocoa powder and stir until well combined. The mixture may look dry at first - keep stirring and it will come together. ¾ cup powdered sugar, ⅓ cup cocoa powder
Stir in the vanilla extract, peppermint extract, and salt. 1 teaspoon vanilla extract, ½ teaspoon peppermint extract, ½ teaspoon kosher salt
Add the flour and cornstarch and stir until no dry flour remains. If needed, use your hands to gently knead the dough in the bowl until smooth. 1¾ cups all-purpose flour, ¼ cup cornstarch
To roll:
Turn the dough out onto a lightly floured surface and knead briefly to form a ball. Divide the dough in half and shape each half into a smooth disc.
Roll the dough to ¼-inch thickness (see tips above in the post about rolling). Cut into rounds using a 3-inch cookie cutter and place cookies 1½ inches apart on the prepared pans.
Gather scraps, reroll, and cut additional cookies.
To chill:
Refrigerate the unbaked cookies for 30 minutes (longer is fine).
To bake:
Preheat the oven to 350°F (175°C).
Bake cookies for 12-14 minutes, until set.
For a nice smooth cookie top, use a flat metal spatual to pat out any bumps or lumps.
Let the cookies cool on the pan for 5 minutes, then transfer to a wire rack to cool completely before decorating.
For the white chocolate “snow”
Line a work surface with a piece of parchment paper, large enough to fit all of the cookies.
Place the white chocolate candy melts and coconut oil (if using) in a small microwave-safe bowl.1 cup white chocolate candy melts, 1 teaspoon coconut oil
Microwave at 50% power in 15-second intervals, stirring between each, until smooth.
Have a second clean small bowl set out near the parchment paper.
Holding a cookie by the edge, dip the bottom of a cookie into the melted chocolate. Turn it a bit from side to side, to create a “snowbank,” then gently scrape excess chocolate on the extra bowl’s rim.
Place cookies on parchment and immediately press a small pretzel piece into the chocolate for the tree trunk.
Allow the chocolate to set completely.
For the buttercream Christmas trees:
Optional: For more uniformly shaped Christmas trees, cut a small triangle from paper or light cardboard in the size you’d like your trees to be. Once the white chocolate “snow” has set, place the triangle in the center of a cookie where you want the tree. Using a small, sharp knife, lightly score along the edges of the triangle to outline the shape. Remove the template and pipe the buttercream just to cover the score lines.(See the video above for a quick demonstration.)
In a medium bowl, stir the butter until smooth.1 tablespoon soft butter
Add powdered sugar, 1½ tablespoons half-and-half, peppermint extract, and food coloring (if using). Stir until smooth, adding more half-and-half as needed for a thick but pipeable consistency. Add green food coloring, just a bit at a time until your desired tree color is reached. Stir well to combine. 1½-2 tablespoons half-and-half, ½ teaspoon peppermint extract, Green food coloring
Transfer buttercream to a piping bag fitted with a small round tip (Wilton #3 works well).
Pipe Christmas trees onto each cookie, starting at the top and widening as you pipe downward.
Immediately sprinkle with nonpareils and top with a decorative star or flower if desired. nonpareils and small decorative stars or flowers
Let cookies dry before storing or packaging.
Notes
Butter softness matters: Very soft butter is essential since no mixer is used.You will have some of the green buttercream left. Peppermint strength varies: Start with the listed amount; adjust slightly if your extract is strong.Half-and-half substitute: Use milk, cream, or a combination of both if half-and-half isn’t available.Storage: Once fully dry (4–5 hours or overnight), cookies can be stacked and stored in an airtight container.