Line an 8-inch /20-cm square pan or a small flat tray with parchment. Split each pitted date open and arrange cut-side up in an overlapping layer, forming an approximately 7-inch /18-cm square.

Cover with a second sheet of parchment. Press firmly with a flat-bottomed measuring cup or a small rolling pin until the dates form a thin, joined base. Remove the top parchment and close any gaps by pressing date edges together.

Spread the stirred tahini in a thin, even layer over the dates. Chill the tray briefly while melting the chocolate so the tahini is less likely to move.

Put chopped chocolate and coconut oil in a completely dry microwave-safe bowl. Microwave at 50% power in 20-second intervals, stirring well after each, about 1–2 minutes total. Stop while a few small pieces remain and stir until smooth; do not add water.

Pour chocolate over the tahini and spread gently to the edges. Scatter pistachios and flaky salt while the coating is wet. Refrigerate about 45 minutes, or until the chocolate is fully set; the exact time depends on thickness and refrigerator temperature.

Lift out using parchment and cut into 12 roughly equal pieces with a sharp knife. Serve chilled. Store covered in the refrigerator for up to 5 days for best texture, or freeze for up to 1 month for quality; let very hard pieces soften briefly before eating.