Line a baking sheet (or two, if you’re making smaller cookies) with parchment paper or a silicone baking mat to prevent sticking and make cleanup easy.

In a large microwave-safe bowl, add the semi-sweet chocolate chips and butterscotch chips. Microwave on medium power (50%) in 30-second increments, stirring after each, until smooth and fully melted, about 1 1/2 to 2 minutes total. Alternatively, melt in a heatproof bowl set over a pot of gently simmering water.

While the chocolate mixture is still warm, stir in the peanut butter, vanilla extract, and sea salt until smooth and glossy. If the mixture seems very thick, warm it for another 10–15 seconds to loosen.

Add the shredded coconut and fold gently until it is evenly coated in the chocolate mixture. Taste and adjust if you want more chocolate or coconut flavor.

Gently add the chow mein noodles, about 1 cup at a time, folding until everything is evenly coated. Try not to crush the noodles too much so you keep the classic haystack texture.

If using chopped nuts, mini marshmallows, or sprinkles, fold them in now, being careful not to over-stir so the noodles don’t break down.

Using a medium cookie scoop or a heaping tablespoon, drop mounds of the mixture onto the prepared baking sheet. Gently press and shape each mound to look like a small haystack, about 1 1/2–2 inches across.

Refrigerate the baking sheet for 20–30 minutes, or until the haystack cookies are firm to the touch. Alternatively, let them sit at cool room temperature for about 1 hour, though chilling is faster and cleaner.

Once set, transfer the haystack cookies to a serving plate or airtight container. Store at cool room temperature for up to 4 days, in the refrigerator for up to 10 days, or freeze for up to 2 months.