Preheat oven to 350 degrees Fahrenheit

Butter an 8x8" square baking pan or 8" round pan

Separate the eggs into whites and yolks

Melt the chocolate and the butter in a small saucepan over low heat

Whip the yolks, vanilla, and sugar together using a mixer until thick, pale, and creamy. About 5 minutes

Add the sifted flour, the melted chocolate butter, and warm milk

Using another mixer, whip the egg whites and lemon juice together until achieving stiff peaks

Carefully incorporate the whites into the yolk mixture in 2-3 additions using a spatula

Pour batter into the greased pan

Bake for 15 minutes. Reduce heat to 300 Fahrenheit and bake for 30 more minutes. Turn off the oven and wait for 10 minutes before removing cake (it should be a little jiggly)

Cool on a rack for 30-45 minutes

Place in the fridge until completely cooled

Cut into squares or rectangles and serve

Enjoy!