Croissant with vegetable butter | Dried Sourdough

Ingredients:

500 g of Manitoba flour
50 g of dried sourdough with yeast Ruggeri Farine
300 ml of warm soy milk
65 g of sugar
250 g of margarine for puff pastry
8 g of salt
1 teaspoon vanilla extract
1 egg for brushing
2 tablespoons of vegetable cream for brushing

Procedure:

Melt the sugar in a saucepan together with the warm vegetable milk.
In the bowl of a stand mixer fitted with a leaf hook, mix the sifted flour with the dried sourdough starter from Ruggeri Farine . Make a hole in the centre and pour in the warm, sweetened milk.
Also add the vanilla essence and a pinch of salt.
Work the ingredients for 10 minutes, at medium speed, until you obtain a smooth and homogeneous dough.
Replace the leaf hook with the hook attachment, and knead the dough for another 10 minutes, at medium/high speed.
Transfer the dough to a lightly oiled bowl and cover with cling film.
Leave to rise in a dry, warm place, away from drafts, for at least 4 hours, until the dough has tripled in volume.
(I let it rise in the oven turned off, with only the light on)
Transfer the risen dough onto a floured work surface and roll out with a rolling pin to form a rectangle slightly larger than the margarine rectangle (20x25 cm).
If you have already rolled out margarine, you do not need to do this step; alternatively, proceed as follows:

between two sheets of baking paper, roll out the margarine into a rectangle.
Place the margarine rectangle in the center of the dough rectangle, then fold the edges of the dough inward, sealing the margarine rectangle.
Seal the ends well by pressing with the rolling pin, to prevent the margarine from leaking out during processing.
Using a rolling pin, roll out only lengthwise, maintaining a rectangular shape.
Fold, bringing the shorter end (bottom side) towards the centre, and repeat with the other end (top) to close the dough, making sure the edge falls underneath the dough itself.
Wrap in cling film and leave to rest in the fridge for 20 minutes.
Remove the dough from the refrigerator, roll it out lengthwise again, repeat the folding process in step 12 (so the bottom side towards the centre, the top side to close the dough).
Wrap in cling film again and place back in the fridge for another 20 minutes.
Repeat step 12 three times, alternating with 20 minutes of rest in the refrigerator.
After repeating the working/resting interval in the fridge three times, take the dough out of the fridge and roll it out lengthwise with a rolling pin, forming a rectangle half a centimetre high.
Cut the rectangle into isosceles triangles.
Make a small cut (about 2 cm long) in the center of the base of the triangle (shortest side).
Lengthen the tip of the triangle by pulling it lightly with your hands, then roll it up starting from the shortest side (base) towards the tip.
Place each croissant thus formed on the baking tray lined with baking paper, spacing the croissants apart.
Cover with cling film or a clean, dry cloth, place them in the oven with only the light on, and leave them to rise for 3 hours.
Once the croissants have risen, brush them with the beaten egg and vegetable cream.
Bake in a preheated oven at 180°C for 20 minutes, in static mode, until golden.
Remove from the oven and let cool completely before removing from the pan.
Store in special bags or in a biscuit tin.