In a separate mixing bowl, beat the eggs, vanilla, sugar and Stevia. Scrape down the bowl as the Stevia can cling to the sides. Should be thicker and almost a custard color.
In a 2 cup glass, liquid measure cup microwave the butter and chocolate chips together 15 seconds at a time, stirring in between each 15 seconds. Continue until smooth and completely melted but not boiling or overheated. It should be warm enough that there are no lumps of chocolate left (approximately a total of 1 minute).
Slowly add chocolate mixture to the egg mixture, beating on low speed. Scrape down the sides. Start mixer again on low speed and slowly add the dry ingredients until well combined.
Pour into prepared 8x8 pan and bake for 25-35 minutes.