Prepare the pan: Line a large rimmed baking sheet or 9 x 13-inch (23 x 33 cm) pan with parchment paper, leaving enough overhang to lift the bark easily after it sets.

Prepare the toppings: Roughly chop the pistachios so you have a mixture of small pieces and larger chunks. Measure the dried cranberries and flaky salt before melting the chocolate.

Melt the chocolate: Place the chopped semisweet chocolate and neutral oil in a microwave-safe bowl. Microwave in 20-second intervals, stirring thoroughly after each interval, until the chocolate is almost completely melted.

Finish melting gently: Stop microwaving while a few small chocolate pieces remain and stir until the residual heat melts them completely. The chocolate should look smooth and glossy rather than thick or grainy.

Spread the chocolate: Pour the melted chocolate onto the prepared parchment. Use a spatula to spread it into an even rectangle about 1/4 inch (6 mm) thick.

Add the pistachios: Sprinkle the chopped pistachios evenly over the chocolate while it is still soft.

Add the cranberries: Scatter the dried cranberries evenly between the pistachios, making sure some fruit reaches the edges of the bark.

Press the toppings lightly: Use clean fingertips or the back of a spoon to press the pistachios and cranberries very gently into the chocolate. They should be partially embedded without becoming covered.

Add the salt: Sprinkle the flaky sea salt evenly over the surface.

Add optional white chocolate: If using, drizzle the melted white chocolate in thin lines over the bark. Avoid spreading it into a solid layer.

Chill until firm: Transfer the bark to the refrigerator and chill for about 1 hour, or until the chocolate is completely firm and no longer gives when gently pressed.

Break into pieces: Lift the set bark from the pan using the parchment. Break it by hand into approximately 20 irregular pieces, or cut it with a sharp knife for neater portions.

Serve or store