Preheat oven to 170c fan-forced. Beat butter, sugar and condensed milk together until light and creamy. Add flour, oats, pecans, chocolate and vanilla extract. Mix well.
Roll 1 1/2 tablespoon portions of biscuit mixture into balls and place onto baking paper-lined oven trays. Flatten slightly.
Cook for 15-18 minutes until just turning golden brown.
Allow to stand on trays for 5 minutes before cooling on a wire rack. Store in an airtight container.