1. Preheat the oven to 200-275°F and line a baking sheet with parchment paper.
2. In a clean, dry bowl, beat room-temperature egg whites with cream of tartar until soft peaks form.
3. Gradually add sugar while continuing to beat until stiff, glossy peaks form.
4. Transfer the meringue mixture to a piping bag fitted with a round tip.
5. Pipe small round discs onto the baking sheet for mushroom caps.
6. Pipe small tall, narrow cone shapes for mushroom stems.
7. Bake in the preheated oven for 45-120 minutes until the meringues are dry and crisp.
8. Remove from the oven and let them cool completely on the baking sheet.
9. Melt a small amount of chocolate and use it to attach the stems to the underside of the caps.
10. Allow the chocolate to set completely to secure the mushrooms.
11. Lightly dust the mushrooms with cocoa powder for a realistic appearance.
12. Store in an airtight container at room temperature for up to 2 weeks.
13. Use as garnishes for yule logs, dessert platters, or woodland-themed treats.