First, melt the butter, sugar, and molasses over a low heat until the sugar dissolves and everything combines.
Let this cool for 5-10 minutes, or until room temperature.
Combine the flour, cinnamon, ginger, cloves, baking soda, and salt in a separate bowl. If using potaske, dissolve it in 1 tsp water in a small bowl and omit the baking soda.
Add the dry ingredients (and potaske, if using it) into the molasses mixture.
Stir together until no dry spots remain.
Wrap the final dough in cling film and place in the fridge overnight (or longer), but it should chill for at least 3-4 hours.
You can also shape the dough into a log and cool it in this shape, if you want to cut out the cookies with a knife instead of rolling them out.
When you are ready to bake the cookies, preheat the oven to 350 F (175 C). Line two or three baking sheets with parchment paper (I do two at a time, but up to you and how much oven space you have).
Take the dough out of the fridge 10-15 minutes before starting to roll it out; it will be very solid.
Prepare a work surface with plenty of flour.
Roll out your dough until very thin (this will make them crispy!), adding flour underneath and over top of the dough as you roll to stop the dough from sticking.
Use cookie cutters to cut out whatever shapes you want. If you cooled the dough in a log shape, just use a sharp knife to cut out round cookies.
Remove the dough from around the shapes (save the scraps!) to make them easier to move to a baking sheet, or just remove the shapes themselves from the dough around it.
Place the cookies on a baking sheet, with a little bit of distance between. These cookies don't spread too much, so you should be able to pack the baking sheets pretty full!
Bake cookies for 6-8 minutes, depending on their thickness. Thin cookies will only take 6 minutes, while thicker ones will take longer. Just keep an eye on them - what you are looking for is a slightly darker color around the edges and on the bottom (but not too dark as this may make them taste slightly burnt!).
When you take the cookies out, they will still be somewhat soft. You can let them cool for a few minutes on the baking sheet before removing and placing on a cooling rack, and when they cool completely they should firm up and become crispy!
Repeat the rolling out process with the scraps and the remaining dough. If the dough starts to get too crumbly, you can discard it!
Cool and enjoy! Store in a cookie tin or tupperware container.