Melt the chocolate in a microwave-safe dish using the chocolate melting function or in 30-second bursts, stirring with a spatula, until smooth. Use a heat-safe basin and swirl repeatedly over boiling water to melt.
Melt the chocolate. Add the olive oil and stir with a spoon or whisk until the chocolate is fully mixed and smooth. Put it somewhere to cool down a bit.
Use a stand mixer or electric whisk to whip egg whites and ¼ cup (50g) sugar on high speed until firm peaks form, approximately 4 minutes.
Fold the melted chocolate into the egg yolk mixture with a broad spatula until incorporated. The mixture will be thick and glossy like brownie batter.
Gradually incorporate one third of the beaten egg whites into the chocolate mixture using a broad spatula. For maximum air retention, fold the mousse gently and rotate the bowl a quarter turn after each fold.