Starts by grinding 1 cup (4 oz/125 g) of pecans with sugar in a food processor until finely ground. Add rice flour, cornstarch, lemon zest, and salt, then pulse to mix thoroughly. Incorporate cold, diced unsalted butter and vanilla extract, pulsing until the mixture resembles a fine meal. Add the remaining ½ cup (2 oz/ 60 g) of pecans and pulse briefly to combine. Finally, add the egg yolk and pulse until the dough begins to form a cohesive ball. Transfer the dough to a bowl and refrigerate until firm, approximately 30 minutes.

Position racks in the upper and lower thirds of the oven and preheat to 325°F (165°C). Line two baking sheets with parchment paper, ensuring a non-stick baking surface.

With hands slightly dampened, shape the chilled dough into 1-inch (2.5-cm) balls. Arrange the balls on the prepared baking sheets, spacing them about 1½ inches (4 cm) apart. Using your fingertip, softly+ create a well about ¼ inch (6 mm) deep in the center of each ball. Optionally, fill the wells with either cinnamon sugar or jam, or divide the cookies, filling half with cinnamon sugar and the other half with jam. Refrigerate the cookies on the baking sheets for 10 minutes to firm up.

Bake the cookies until they begin to show color and the turn light brown, approximately 15 minutes. Allow the cookies to cool on the baking sheet for 2 minutes before carefully transferring them to wire racks to cool completely. Store the cooled cookies in an airtight container at room temperature for up to 5 days.