Apples, leaven and cinnamonrolls

Have you ever baked using leaven? I've done it at a couple of times, but only bread and it's always turned out good. But! I've always used yeast and today I learned there's another way to do it - with grated apples. It takes longer, 5 days, but I am so curious!
It was a recipe for cinnamon rolls that used apples for the leaven, and I just have to try it! I thought I'd share the recipe with you. <3

Basic leaven

1 apple (grated)
100 g water (35 degrees celsius)
200 g flour

Leave in a glass container with the lid ajar in a warm place for three days. Shake it each morning and evening.

Day four you add 200 g water and 200 g flour, stir and rest a one or two more days. You know have a leaven that you can keep in the fridge until you decide to use it. :) Take good care of it, and keep adding water and flour (equal amounts of each) now and then and the day before you plan on using some of it. If you take good care of your leaven it's said you can have the same one for years! I suppose that's how they did it in old days.

Cinnamon rolls

500 g milk
1100 g flour
200 g sugar
200 g butter (room temperature)
30 g yeast
20 g ground cardamom
10 g salt
50 g of your leaven

Filling

250 g butter
250 g sugar
Cinnamon

For decoration

1 lightly whipped egg (for brushing the rolls)
Sugar for decorating rolls (in Swedish: pärlsocker)

To make good rolls, you have to work the dough thoroughly. If you have a machine, that's great! But if you don't, it will take a bit of effort. Work the dough for at least 10 minutes, until you can stretch the dough so thin it gets transparant without it breaking.
Using a rolling pin, make a large rectangular shape (about 60x40 centimeters), mix butter and sugar and gently apply it over the entire dough. Sift cinnamon over ackording to taste. Now take both of the edges, and fold them to the middle, then fold it again like a book.
Cut into pieces that are as wide as your little finger, and twist them into knots. Let rise for 2 hours, brush with the egg and decorate with the sugar. Bake in the oven for 15 minutes (200 degrees celsius) until they are golden brown. <3 Done!