Heat the cream to 80°C, pour over the chocolate, wait 1 minute, then whisk until smooth and fully emulsified.
Combine all ingredients in a bowl. Blend with an immersion blender, keeping the head fully submerged, until completely smooth and paint-like in texture. Avoid incorporating air.
Cover and refrigerate until the batter reaches 3–4°C, about 2 hours.
In a mixing bowl, combine softened butter, brown sugar, salt, flour and cocoa powder. Mix until fine crumbs form.
Add the egg and quickly knead into a dough. Shape into a flat disc 1–2 cm thick, wrap and refrigerate for 1 hour.
Preheat oven to 160°C (320°F). Roll out dough to 3 mm thickness, prick with a fork and bake for 15 minutes. Cool completely.
Crush baked dough into fine crumbs, mix with softened butter and firmly press into the bottom of the prepared pan. Refrigerate for 10 minutes
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