Cream butter, sugar, and brown sugar until light and fluffy.
Beat in the egg and then gently mix in sourdough starter.
Mix baking soda with boiling water and add molasses (mixture will fizz).
In a separate bowl, whisk together all-purpose flour, buckwheat flour, soft wheat flour, spices, salt, pepper, and cardamom.
Add dry ingredients alternately with the soda-water, molasses mixture to the butter mixture, mixing until combined.
Chill dough for at least an hour (or overnight).
Let the dough sit out to warm until it's pliable enough to roll.
Preheat your conventional oven to 375°F (190°C) or a convection oven to 350°F (175°C).
Roll out the dough to 1/4 inch thickness and cut into desired shapes.
Place the cookies on a baking sheet and bake in the preheated convection oven for about 10 minutes in a convection or 14 minutes in conventional or until golden brown.
Let cool on a wire rack before consuming or decorating.