In a large bowl, cream butter and brown sugar until light and fluffy. Beat in eggs and vanilla. Combine the flour, salt and baking soda; gradually add to creamed mixture and mix well. Divide into four portions. Refrigerate until chilled.
In a large saucepan, bring the dates, sugar and water to a boil. Reduce heat to medium; cook until mixture is thickened, about 15 minutes. Cool completely. Stir in pecans.
On a baking sheet, roll out each portion of dough between two sheets of waxed paper into a 12-in. x 9-in. rectangle. Refrigerate for 30 minutes.
Remove waxed paper; spread with date mixture. Tightly roll up each portion jelly-roll style, starting with a long side; wrap in plastic wrap. Refrigerate for 2 hours or until firm.
Unwrap and cut into 1/4-in. slices. Place 1 in. apart on greased baking sheets. Bake at 350° for 10-12 minutes or until set. Remove to wire racks to cool. Store in an airtight container at room temperature, or freeze for up to 3 months. Yield: 16 dozen.