Preheat oven to 350°F (177°C). Line an 8 x 8 inch baking pan with parchment paper.
Add eggs to a stand mixer with wire whisk attachment. Beat at highest speed for 8 minutes or until eggs turn thick and pale yellow and should be at least triple in volume. When you lift the beater, the mixture that drips off should be able to stay on top of your egg batter for several seconds before sinking back in. See photo in post for reference. This can be done with a hand mixer but it may take more time.
While your eggs are beating, melt your chocolate. Add chocolate to a large microwave-safe bowl and heat in 30 second intervals, stirring in between with a spatula, until chocolate is completely melted and smooth. You do need to be careful to not overcook your chocolate. If your chocolate is close to being fully melted but needs a little more heat, heat for only 15 seconds instead of 30 seconds. You can also melt the chocolate on the stove using the double boiler method.
Fold your egg mixture into the chocolate in 3 batches. First, add in 1/3 of the egg mixture to the chocolate. Use your spatula to gently fold in the egg mixture. Make sure to scoop the chocolate from the bottom of the bowl so that all the chocolate gets incorporated. Fold until no egg streaks remain. Repeat with second third of egg mixture and then final third of egg mixture. It's okay if you have some small chunks of chocolate in your batter. Finally, gently stir in the lemon juice until just incorporated.
Pour batter into prepared pan. Bake for about 25 minutes or until surface is browned and toothpick inserted comes out clean. Let brownies cool completely to set. Wait until brownies are cooled and set before slicing into squares with a sharp knife. If desired, dust with powdered erythritol before serving.
Notes
I used Lily's no sugar added white chocolate chips. They are sold in 9 oz bags and you will need one full nine-ounce bag for this recipe.
I have only tested this with fresh lemon juice. You should only need one lemon to yield 2 oz of lemon juice. 2 oz equals 4 tbsp of lemon juice. I don't recommend adding lemon zest to the brownies because the brownies are not super sweet so the bitterness of the zest is a little too much.
Do not add lemon juice until the end. If you add it early, it will cause your chocolate to seize.
You want to use your egg mixture very soon after it is done, otherwise it will deflate and lose air. If you are beating with a hand mixer, I recommend doing it after your chocolate is melted, so that your egg mixture can be used right away. You may need a few more minutes of beating when using a hand mixer to reach the right consistency.
These brownies work best in an 8 x 8 inch pan or smaller. If you bake in a bigger pan your brownies will be too thin.
If you are on a keto diet, please remember to look at net carbs and not just total carbs in the estimated nutrition. The net carbs count excludes fiber and sugar alcohols (carbs from erythritol).
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.