Prep the oven and pans: Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper for easy cleanup.

Cook and mash the sweet potato (if needed): Pierce a medium sweet potato with a fork and bake at 400°F (205°C) for 45–60 minutes until tender, or microwave 6–8 minutes, turning once. Scoop out the flesh and mash until smooth. Let it cool completely. You’ll need 1 cup.

Cream the butter and sugars: In a large bowl, beat the softened butter, 3/4 cup granulated sugar, and 1/4 cup brown sugar until light and fluffy, about 2–3 minutes. This step helps your cookies lift and stay soft.

Add the egg and vanilla: Mix in the egg and vanilla until combined. Scrape the bowl so everything blends evenly.

Add the sweet potato: Stir in the mashed sweet potato. The mixture may look slightly curdled at first; that’s fine. Mix until smooth and uniform.

Whisk the dry ingredients: In a separate bowl, whisk flour, baking powder, baking soda, salt, 1 1/2 teaspoons cinnamon, and nutmeg.

Combine wet and dry: Add the dry ingredients to the wet mixture. Stir just until you no longer see dry flour. The dough will be soft and slightly sticky, more like a thick batter than a stiff dough.

Make the cinnamon sugar: In a small bowl, combine 1/3 cup sugar with 1 teaspoon cinnamon.

Scoop and roll: Use a 1 1/2-tablespoon scoop (or heaping tablespoon) to portion dough. Roll each portion in the cinnamon sugar and place on the prepared sheets, spacing about 2 inches apart.

Gently flatten: Lightly press each dough ball to about 1/2 inch thick. This helps them spread evenly.

Bake: Bake 10–12 minutes, until the edges are set and the tops look slightly puffed and dry. They may seem soft in the center; they’ll finish setting as they cool.

Cool: Let cookies rest on the baking sheet for 5 minutes, then move to a rack to cool completely. The texture improves as they cool.