Line an 8×8 inch square dish with wax paper and then slightly oil the paper. Combine butter and heavy cream in a small saucepan on low heat until it begins to simmer. Remove from heat and set aside.

In a large saucepan, melt sugar, water, and corn syrup together on medium-high heat, until mixture dissolves, begins to bubble and turns slightly brown in color (350 degrees F on a candy thermometer).  Remove from heat and gently stir in the cream mixture.

Place back on the burner and boil, stirring vigorously, until the mixture reaches 248 degrees F (about 10 minutes). Pour into prepared 8×8 dish, then let sit at room temperature until cooled and slightly firm.

After 1 1/2 hours, invert dish onto cutting board. Peel off wax paper and cut into 1×2 inch rectangles. Sprinkle with fleur de sel and wrap in 4×5 inch wax paper squares.