Heat the oven to 350 F. In a medium bowl, sift together the sugar, flour, cocoa powder, baking soda, baking powder and salt. In a mixing bowl, add the yogurt. Turn the mixer to low speed and alternate adding the dry ingredients and the eggs to the bowl. Slowly add the coffee and vanilla to the mixture. Continue mixing until the batter is smooth. Coat two 8-inch round cake pans with nonstick spray and pour equal amounts of batter into each cake pan. Bake for about 30 to 35 minutes until toothpick comes out clean when inserted into the center of the cakes.