Step 1

Preheat oven to 350 F. Spray an 8-inch square pan with nonstick spray.

Step 2

In a microwave-safe bowl, melt chocolate squares and butter for 1 to 2 minutes in microwave until melted and smooth, stirring every 20 seconds.

Step 3

Whisk both sugars into the chocolate mixture. Add eggs, one at a time, and mix well after each addition. Mix in flour and vanilla. Pour the into the prepared pan.

Step 4

Bake for 40 minutes or until a toothpick in center comes out clean. Cool completely on wire rack. Cut into squares and serve.