1) Preheat the oven to 350°F. Lightly grease (or line with parchment) a 9" x 13" pan.
2) To make the squares: In a medium-sized mixing bowl, whisk together the flour, ginger, allspice, salt, baking soda, and crystallized ginger.
3) In a separate bowl, stir together the molasses, eggs, brown sugar and butter.
4) Combine the wet and dry ingredients, beating till smooth.
5) Spread the batter in the prepared pan, and set it aside.
6) To make the streusel topping: Using a pastry blender, electric mixer, or your fingers, mix together the flour, butter, salt, and brown sugar till it's fairly well-blended; some chunks of butter can remain. Mix in the crystallized ginger.
7) Bake the squares for 15 minutes. Sprinkle on the streusel, and bake an additional 30 minutes, till the streusel is a deep, golden brown.
8) Remove the squares from the oven, and run a knife around the edges of the pan to loosen them. Allow them to cool, then cut into 2 1/4" squares.
Yield: about 2 dozen squares.