Heat water, molasses, and shortening to 120°F (50°C).

Combine rye flour, 1/2 cup all-purpose flour, cocoa, caraway seeds, flax seeds, yeast, sugar, and salt.

Stir in the shortening mixture to the flour mixture.

Gradually add remaining all-purpose flour until a soft dough forms.

Knead the dough for 8-10 minutes until smooth and elastic.

Place dough in a greased bowl, turning to coat.

Cover and let rise for 30-60 minutes, until doubled.

Punch down dough and roll into a 14x12-inch rectangle on a floured surface.

Place the dough on a greased baking sheet.

Spread mustard lengthwise in a 3-inch strip down the center of the dough, leaving a 1-inch border.

Layer meat, sauerkraut, and cheese on top of the mustard.

Make diagonal cuts 1 inch apart almost to filling along one side of dough.

Repeat on the other side in the opposite direction.

Fold strips over filling, alternating sides, to resemble a braid, overlapping the ends.

Brush with egg white to seal.

Cover and let rise for 30-40 minutes, until doubled.

Brush top with remaining egg white.

Sprinkle with caraway seeds.

Bake at 350°F (175°C) for 30-40 minutes, until puffed and dark brown.

Remove from pan and let cool slightly on a rack.

Serve warm or let cool completely.