Filling
Combine figs, dates and raisins in a food processor bowl fitted with a steel blade and process to finely chop. Place mixture in a medium bowl and add remaining filling ingredients; stir to combine.
Cover and refrigerate for at least 8 hours.

Dough
Whisk flour, sugar, baking powder and salt in a large bowl to combine.

Add butter and blend with your fingertips until mixture resembles coarse meal. Set aside.

Beat egg, milk and vanilla together in a medium bowl. Add to dry mixture and stir to make a rough dough.

Turn dough onto a lightly floured surface and knead until smooth, about 5 minutes. Divide dough into 4 pieces. Cover and refrigerate for 45 minutes.

Preheat oven to 350 degrees. Lightly grease 2 large baking sheets.

Combine water and egg white in a small bowl and beat slightly to make an egg wash.

Roll one piece of dough at a time into a 12" square on a lightly floured surface. Cut dough into 4" x 3" rectangles. Spoon 2 tablespoons of filling lengthwise down the center of each rectangle. Fold the long sides of each rectangle inward to the center to enclose the filling; pinch edges to seal. Turn rectangle log seam-side down and press gently to flatten seam.

Brush egg wash on log and sprinkle with nonpareils. With a floured knife, cut log crosswise into 1½"-wide slices and arrange ½" apart on prepared baking sheets.

Bake 15 minutes. (The cookies will not brown.) Transfer cookies to wire racks to cool.