London, here is one recipe for hardtack bread which was previously posted on TKL by eggy. She has posted many wonderful recipes on TKL. You will find more hardtack recipes if you type hardtak in the "find a recipe" box here at TKL. Each recipe seems a bit different. Gives you a variety from which to pick. Hope this helps
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From Beatrice Ojakangas "Scandinavian Cooking"

Oatmeal Hardtack(Knackebrod) Sweden

1/2 cup vegetable shortening
1/4 cup butter, room temperature
1/2 cup sugar
2 cups uncooked rolled oats
3 cups all-purpose flour
1 1/2 t salt
1 t baking soda
1 1/2 cups buttermilkIn a large bowl cream shortening, butter and sugar until smooth.

In a medium bowl combine oats, flour, salt and baking soda.

Alternately add flour mixture and buttermilk to creamed mixture, blending until stiff like a cookie dough. Refrigerate 30 minutes. Grease a large baking sheet; sprinkle with rolled oats. Preheat oven to 325 F (165C.

Divide dough into 8 portions. Shape each into a smooth ball. Return 7 balls to bowl; cover and refrigerate. Place remaining ball of dough on prepare baking sheet. Flatten as much as possible with your hands, then use a rolling pin to roll dough to edges of baking sheet. Using a hardtack rolling pin

(doesn't everyone have one of these???) make pebbled imprints on top or prick evenly with a fork to make a rough texture. Using a pastry wheel, knife
or pizza cutter to score in 2 " squares.

Bake 15-20 minutes or until crisp and golden. Cool 3 minutes on
baking sheet,
and then place on a rack to finish cooling. Break into crackers where
scored.
Repeat. Makes about 128 crackers.