Place butter in a large bowl. Using a wooden spoon, gradually beat in sugar until creamy. Gradually stir in flour just until mixed.
Preheat oven to 300F (150C). Place pistachios in a small bowl. Pinch off about 1 tbsp (15 mL) dough and form into a ball. Lightly roll in pistachios. Place on an ungreased baking sheet. Repeat with remaining dough, placing 1 inch (2.5 cm) apart until sheet is filled. Make an indent in centre of each using your pinky.
Bake in centre of preheated oven until edges are golden, 15 to 18 minutes. Remove cookies to a cooling rack. Repeat with remaining dough and nuts. Refrigerate up to 1 week or freeze up to 1 month. Just before serving, fill each cookie with 1/2 tsp (2 mL) jam or lemon curd.
Nutrition (per serving)
These are a great make-ahead option. Prepare and bake the dough, then fill with colourful jams or lemon curd just before serving.