In a stainless steel saucepan put margarine cut into small cubes, then place the saucepan on a steam bath, stir until the margarine is melted. Transfer the melted margarine in a bowl, add the sugar and start mixing for 5-6 minutes, then add the vanilla essence, baking powder, salt and mix. Pour mineral water and then flour little by little until you get a dough not very hard but not sticky.
Wrap the dough in cling film and refrigerate for 30 minutes. After 30 minutes, take the dough out of the fridge, divide it into several balls and spread the dough with a rolling pin, not very thick, then with the help of a plate cut a circle, cut into 8 triangles. Place the jam and form the croissants.
In the stove tray, lined with baking paper, place the croissants, heat the oven to 180 degrees C and bake the croissants until they start to brown nicely on the edges. Remove from the oven, roll in sugar or leave as is, each as you prefer.