Step 1To make the chocolate sauce, in a small, heavy saucepan, combine the chocolate and water over low heat, stirring often, until the chocolate is melted and smooth, about 3 minutes. Remove from heat and stir in the butter and vanilla. This makes 1 cup chocolate sauce, which will keep, covered and refrigerated, for 3 to 5 days. Rewarm before using.
Step 1In a large chilled bowl, whip the cream with the sugar and vanilla at medium-high speed until stiff. Refrigerate the whipped cream until ready to use, or up to 30 minutes.
Step 1Cut the strawberries in thick slices lengthwise; you will have about 4 cups. Put them in a large shallow bowl and sprinkle them with sugar. Mix gently. Refrigerate them until ready to use, up to 30 minutes.
Step 2Using a serrated knife, carefully cut off the top half of each puff and reserve this part as a "hat."
Step 3Fill the puffs: Using a pastry bag fitted with a large star tip, pipe the whipped cream generously onto the bottom of each puff, allowing the cream to show at the sides. Top with a layer of strawberries, allowing the berries to extend slightly over the edges. Pipe another layer of whipped cream over the berries. Set the pastry hats on top.
Step 4Drizzle the tops of the profiteroles with chocolate sauce. If the sauce becomes too thick to drizzle, reheat it over low heat, stirring, until it becomes more fluid.
Step 5Garnish each chocolate-drizzled puff with a pinch of minced pistachios.