Combine flour, salt and baking soda in a bowl. Cut in the margarine until crumbly. Mix lemon juice into pareve milk and let stand for five minutes.

Add egg and pareve milk mixture to flour and knead until stiff dough forms. Add more flour, if needed.

Roll out dough on a floured surface to 1/8-inch thickness.

Cut into squares and place on lightly greased baking sheet. Prick with fork in a few spots. Sprinkle with coarse salt, if desired.

Bake at 400 degrees Fahrenheit for 10 minutes or until lightly browned.