Stir the dried yeast and sugar into the warm water and allow to stand for 10 minutes or until foam forms on the surface. Stir until the yeast dissolves.
In a saucepan, add the soy milk, margarine and mashed potatoes and cook over low heat until the margarine has melted and the mixture is well combined. Stir in the yeast mix.
Stir the sugar, salt and 1/2 the flour into the yeast and soy milk mixture. Gradually knead in the remaining flour either with the hand mixer dough hook or by hand. If the dough is too sticky knead in more flour.
Knead for approximately 10 minutes, until dough is smooth. Cover with a damp towel and leave dough to stand for one hour in a warm place until its volume has doubled.
Knead dough and then roll out on a floured work surface to a circle about 40cm in diameter. Cut the circle into 16 equal triangles. Roll the triangles from the wide side to the point into croissants.
Bake the croissants for about 15 minutes until they are a light golden brown colour. Take care not to bake them for too long or let them get too dark otherwise they will dry out. If desired, brush with melted margarine while still hot.