To begin, dissolve the yeast in lukewarm water. If using honey or dark syrup, stir it in at this stage to help activate the yeast. Let the mixture sit for5–10 minutes until slightly foamy. This ensures the yeast is active, which is essential for proper fermentation.

In a large bowl, combine the rye flour, plain flour, and salt. Create a well in the centre and pour in the yeast mixture along with the buttermilk. Using a wooden spoon or your hands, gradually mix until a sticky dough forms. Rye flour absorbs moisture differently from wheat flour, so if the dough feels too dry, add a tablespoon of water at a time until it holds together.

Turn the dough onto a lightly floured surface and knead for about 5 minutes. The dough will be dense and slightly rough, this is normal for rye based doughs. Unlike wheat dough, it won’t develop much elasticity due to the lowergluten content, so kneading is more about ensuring even hydration rather thanstretchiness.

Cover the dough with a clean kitchen towel and let it rest at room temperature for about 1 hour. This resting period allows the natural fermentation to develop the characteristic sour flavour. For a more pronounced tang, leave it to rest for 2–3 hours.

Preheat your oven to 200°C (fan assisted)or 220°C (conventional oven). If you have a baking stone or an inverted baking tray, place it inside to heat up, this will help create a crispier texture.

Divide the dough into 4 equal portions. Roll each portion out as thinly as possible (about 1–2mm thick) on a lightly floured surface. Use a fork to prick the dough all over, this prevents air bubbles from forming and ensures an even bake. Traditional hapankorppu often has a dimpled surface, which can be achieved using a texturedrolling pin if available.

Carefully transfer the rolled out dough onto a baking sheet lined with parchment paper. If you’re baking multiple pieces at once, leave a small gap between them. Optionally, you can sprinkle a light dusting of rye flour on top for extra texture.

Bake in the preheated oven for 15–20minutes, or until the crispbreads are dry and slightly browned around the edges. If you prefer an ultra-crispy texture, turn off the oven and let them sit inside with the door slightly ajar for another 10 minutes.

Let the hapankorppu cool completely on a wire rack before storing. Thesecrispbreads develop their signature snap once fully cooled. Serve them plain, with butter, cheese, or a traditional Finnish topping like smoked salmon or reindeer meat. Store in an airtight container to maintain crispness for up to two weeks.