The Greek Orthodox liturgy uses a particular bread which is made solely for liturgical use. Prosphoron (plural: prosphora), which literally means offering, is made by members of the congregation from four ingredients: flour, salt, water, and yeast, though some streams in the Orthodox tradition omit the salt. The leavened dough is shaped into two round pieces which are stacked on top of one another and baked. The two pieces of dough symbolize Christ's two natures: human and divine.
In the Greek tradition, one large loaf is used in the liturgy. In the Slav tradition, there are five loaves, remembering the loaves that fed five thousand people.
Before baking, the bread is stamped with a seal called a sphragis or Panagiari. The stamp's design usually includes the abbreviation IC XC NIKA (Jesus Christ conquers) and the shape of a cross. The stamp below was available for purchase at the time of this post's publication.
One additional ingredient not mentioned above is prayer. The process of baking prosphora is a prayerful process. When preparing to bake, kneading the dough, stamping the loaf, and putting the loaves in the oven, the baker prays. Scripture reading is encouraged while the bread is baking. The tools and utensils for baking prosphora are often kept separate from other kitchen tools so that they are used only for prosphora.
An internet search will yield a number of recipes for Prosphora.