Spray 8- or 9-inch square baking pan with cooking spray.
Combine corn syrup, 1 cup cream, milk, sugar and salt in a 4-quart saucepan. Bring to boil over medium heat, stirring occasionally.
Reduce heat to medium-low and continue cooking (at a low boil) and stirring occasionally until temperature on candy thermometer reaches 234°F or small amount of mixture dropped into very cold water forms a soft ball which flattens on removal. This will take about 40 minutes.
Gradually add remaining 1 cup cream in a thin steady stream, stirring constantly.
Continue cooking over medium-low heat, stirring frequently until temperature on candy thermometer reaches 244°F or small amount of mixture dropped into very cold water forms a firm ball which does not flatten on removal. This will take about 30 minutes. Remove from heat.
Stir in nuts and vanilla. Pour into prepared pan. (NOTE: Do NOT scrape side of saucepan.) Cool on wire rack for at least 1 hour until caramel is room temperature.
Invert cooled candy onto cutting board. If candy sticks, heat bottom of pan slightly to release from pan; cool before cutting. Cut into 1-inch squares. Wrap squares individually in waxed paper or plastic wrap. Store in tightly-covered container.