Line a sheet pan with parchment paper and set aside.
Melt the butter in a large skillet over medium heat. Add the kataifi and stir until it turns golden brown.
Place the chocolate in a large microwave-safe bowl and melt it in the microwave in 30-second intervals, stirring after each interval, until fully melted. Add the pistachio butters and tahini to the melted chocolate. Once the pistachio butter is fully incorporated, stir in the toasted kataifi.
Spread the chocolate mixture evenly on the prepared sheet pan.
Transfer the remaining pistachio butter to a Ziploc bag, cut off the tip of one corner, and drizzle the nut butter over the chocolate. Gently tap the sheet pan on the counter to help the layers blend. Refrigerate for at least 1 hour, or until the chocolate has set.
Break the bark into bite-sized pieces and serve.