Preheat oven to 350 degrees F. If using a glass plan, preheat your oven to 325 degrees F. Prepare, grease and flour your baking pan.

In the microwave, place unsweetened chocolate and butter in a glass measuring cup or glass bowl and heat until almost melted. Stir to melt remainder. You could also melt in saucepan on stove over low heat.

Place eggs, sugar and vanilla in large bowl and using an electric mixer blend until light colored and combined. Stir in the chocolate/ butter mixture and blend. Next, add the flour and blend. Gently blend with a spoon or spatula. Do not overbeat.

Pour mixture into prepared baking pan. Spread chocolate chips over the top and using a knife swirl around the batter to immerse some of the chips.

Bake for 30-35 minutes or until knife inserted comes out clean. Cool on rack completely before cutting. Store in a airtight container. May freeze for up to one month.