Delicious Home-Made Brownies From Scratch

My sister is in town again. This time, she brought her baking skills with her. This is a favorite recipe of hers.
INGREDIENTS
4 oz (1 box) unsweetened chocolate
1 1/2 sticks of butter
1 cup self-rising flour
3 eggs
2 cups white sugar
1 tsp vanilla
DIRECTIONS
Preheat oven to 350.
Grease a 9×13″ pan with butter or cooking spray.
Make sure oven rack is in the middle of the oven.
In small microwave safe bowl, melt butter and chocolate in microwave (or over double boiler). Allow to cool slightly.
In larger mixing bowl, beat eggs thoroughly. A whisk is fine.
Gradually add sugar.
Blend chocolate mixture and vanilla into egg/sugar mixture.
Add flour, stir well.
Spread in the greased 9×13″ pan and bake for 25-30 minutes.
Cool and cut into 24 squares.