What is the key for achieving right consistency for caramel in tart? Too thin caramel for tart, not sauce.

I made the Claudia Fleming's Chocolate Caramel Tart with Fleur de sel from Amanda's Essential NY Times Cookbook. It smelled wonderful and looked amazing but when I cut a slice out of the round tart, the caramel ran slowly and puddled onto now empty spot on the tart pan. I'm not sure it's supposed to be that runny or it needs to be thicker and more set. It wasn't as runny as caramel sauce that you'd drizzle over ice cream but didn't seem thick enough for this tart. This caramel called for just suar and corn syrup in the beginning- no water. Later you add heavy cream, unsalted butter. What is the key for making the caramel that is right consistency but not overlooked/burnt and sour ?