In a medium bowl, cream the butter and sugar with a hand mixer until light and fluffy.
2. Step
Add the egg and vanilla extract and mix until fully incorporated.
3. Step
Add the flour, baking soda, and baking powder, and mix until the dough is crumbly, but holds together when squeezed.
4. Step
Split the base dough in half, add your desired mix-ins, and incorporate them fully.
5. Step
We used chocolate hazelnut spread and cocoa powder for one half and peanut butter for the other.
6. Step
Roll out each dough between two sheets of parchment paper until it’s ¼-inch (6-mm) thick. Chill both doughs for 30 minutes.
7. Step
Place one half of flavored dough on top of the other and start to roll up the doughs into a swirl. Wrap the roll in plastic wrap and chill in the fridge until solid, about 4 hours.
8. Step
Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.
9. Step
Once chilled, unwrap the dough, slice into ½-inch (1 cm) thick coins, and place them on the baking sheet at least 2 inches (5 cm) apart, as the cookies will spread while baking.
10. Step
Bake the cookies for 10 minutes. Let cool at room temperature for about 30 minutes.
