In a heavy 1-quart saucepan, combine cream and sugar.

Place pan over medium-high heat and bring mixture to a simmer, whisking until sugar is dissolved. Reduce heat to low.

Gradually add chocolate chips, a small bit at a time, whisking until each addition is completely melted into the cream before adding more.

When all chocolate is added and melted, add butter. Continue cooking, whisking constantly, until the butter is incorporated into the sauce. Remove from the heat.

Serve immediately, still warm, or allow to cool and store in the refrigerator, in an airtight container, until ready to reheat for serving. (See Notes 4 & 5 Above)