Preheat oven to 350°F. Line a 9 in baking sheet with parchment, leaving overhang on sides
Chop chocolate and melt in double boiler over low heat, together with butter, stirring frequently to blend until smooth
Whisk eggs, olive oil and sugar for 2-3 minutes, then add the molten chocolate/butter and whisk until smooth
Sift together all dry ingredients and fold them into the chocolate batter
Pour batter into pan. Sprinkle with sea salt (or walnuts, if desired). Bake for 25 minutes. Cool for 1 hour before cutting