Preheat oven to 350 degrees.
With a mixer, beat the eggs with the sugar until slightly thickened and light in color, about 5-7 minutes. The mixture should almost double in size. The eggs work as your leavening agent in this recipe, so do not skip this step. This mixture should form a ribbon when you lift the beaters out of the bowl.
Add the butter and vanilla; mix two more minutes.
Stir in the flour until just combined.
Add the cranberries and stir to mix throughout.
Spread in a buttered 9x13 pan. Bake for 40-50 minutes, or until very lightly browned and a toothpick inserted near the center of the cake comes out clean.
Let cool completely before cutting into small slices.