- With the rack in the middle position, preheat the oven to 350°F (180°C). Line two baking sheets with parchment paper or silicone mats.
- In a food processor, pulse the pecans until finely chopped.
- In a large bowl, cream the butter and sugar with an electric mixer. Add the egg and liqueur and mix until smooth. With the mixer at low speed, or using a wooden spoon, gradually stir in the pecans and flour.
- Using a 1-tbsp ice cream scoop, shape the dough into balls. Roll them between your hands and place on the prepared sheets, spacing them evenly.
- Bake one sheet at a time for 12 minutes or until the cookies are light golden brown. Let cool completely on the baking sheets.
- Place the icing sugar in a bowl. Coat the cookies in the icing sugar. Shake off any excess, then coat again. The cookies will keep for 2 weeks in an airtight container at room temperature.