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1
Heat the heavy cream to just below a simmer — it must not boil. Pour the hot cream over the chopped couverture in a bowl. Allow to stand undisturbed for 2 minutes; the chocolate softens evenly in the steam before any stirring begins.
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2
Stir from the centre outward in slow, expanding circles — the ganache technique, preserving the emulsion throughout. Work patiently; the mixture should become smooth, dark, and unified before the edges of the bowl are reached.
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3
Add the butter piece by piece, incorporating each fully before adding the next. Stir in the sea salt and the tablespoon of strong coffee. The sauce is ready when it is fluid, glossy, and flows smoothly from a spoon — at approximately 50 °C it coats without pooling and without running thin.
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4
Slit each choux bun on its side with a small cut — sufficient to allow filling, not enough to split the bun structurally. Fill each bun generously with a scoop or quenelle of vanilla ice cream. Arrange the filled buns in a serving bowl or in individual dishes.
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5
This is where the dish lives or dies: pour the hot chocolate sauce over the filled buns immediately before service and to order only. Pre-filled buns soften; pre-poured sauce cools; the preparation does not wait. The sauce, still hot, will produce an audible soft sizzle on contact with the cold ice cream as a thin layer of chocolate momentarily solidifies — this sound confirms that both components are at the correct temperature. The sauce should flow in a dark, glossy film across the buns and ice cream. Serve at once.