1. Line a 9X5-inch (23X12cm) loaf pan with parchment paper. Set aside.
2. In a bowl stir cocoa powder and cornstarch, gradually add 1 cup (240ml) of milk, while constantly whisking, until incorporated and smooth. Strain through a fine sieve and set aside.
3. In a large pot combine 3 cups of milk, cream, sugar and salt. Place the pot over low-medium heat and let the sugar dissolve. Then pour in the cornstarch mixture and cook, over medium heat, stirring constantly until thickens, about 8-10 minutes. Turn the heat off, add chopped chocolate and stir until melted and combined. Strain through a fine sieve (optional).
4. Pour the batter into prepared pan, let cool to room temperature, then refrigerate for at least 6 hours.
5. Before serving dust with cocoa powder.
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