Lightly oil 4 baking sheets. In a large heavy saucepan, combine the cream, sugar and orange zest. Bring to a boil over moderately high heat, stirring constantly with a wooden spoon. Cook, stirring constantly, until the mixture registers 240° on a candy thermometer; this can take up to 50 minutes. The mixture will be thick, bubbly and golden brown. Add the pecans and cook, stirring, for 3 minutes.
Meanwhile, place a large bowl of cold water in the sink. Remove the pan from the heat and place the bottom in the cold water for 5 seconds to stop the cooking. Using 2 spoons, drop tablespoon-size pralines onto the oiled baking sheets, spacing them 1 inch apart; let cool completely.
The pralines can be stored between sheets of wax paper in an airtight tin for up to 1 week.