Dissolve the yeast in a bowl; add the lukewarm water and one spoonful sugar from the recipe and as much flour as necessary to have a thin dough (about 150gr). Stir very well. Cover the bowl and leave in a warm place for about 20 minutes. In a small pot -at very low temperature or in bain-marie- melt the butter, add the sugar and stir well until the sugar dissolves. Add the eggs and whisk fast. Using a mortar, crush the “mahlepi” (mahlab) the mastic and the seeds of “kakoule” (cardamom) with one spoonful sugar (from the sugar of the recipe). Sift the flour in a bowl. Add the yeast and the mixture of egg-butter-sugar. Add the cardamom, mahlab and mastic and knead until the dough does not stick. Cover the bowl with the dough and leave rise (to double in volume) for about an hour. When the dough rises, separate, in three parts. Knead into a braid. Place in a pan, on non stick paper and cover again to rise and double in volume. Before baking, coat the “tsoureki” with beaten egg and water.