I use the metric system in my blog for different reasons.

I grew up in Denmark and we use the metric system.
When you bake you need to be accurate, and imperial messurements are not very accurate. Try to weigh a cup of all-purpose flour sifted and unsifted, there is a big difference.

I will be using table- and teaspoons measurements.

Liquids:

Potaske is Potassium carbonate (K₂CO₃). You can replace potaske with Baking Soda, but the cookies won't be as crispy.

Natron is Baking Soda.

Hjortetaksalt is Ammonium bicarbonate (NH₄HCO₃). You can get it here

Yeast:

1 pack of danish live yeast is 50 g, equivalent to 1 pack of Danish dry yeast, 11.8 g.

1 pack of Danish dry yeast is 11.8 g, which is equivalent to 4 teaspoons dry yeast.

1 pack of fleischmann's dry yeast contains 7 g.

Butter:

½ cup butter = 1 stick = 113.4 g