Compressed yeast and dry yeast can be used interchangeably in baking. Use one package, which is about 2 1/4 teaspoons, of active dry yeast for 1 (0.6-ounce) cake of compressed yeast.
Compressed, or fresh, yeast may be softened in liquid or crumbled directly into the dry ingredients, according to recipe directions. Dry yeast is generally dissolved in warm water prior to use. Again, though, be sure to follow recipe directions.