1. Place rack in center of oven. Heat oven to 375 degrees. To make the crust: In the bowl of an electric mixer fitted with the paddle attachment, mix butter and brown sugar on medium speed until light and fluffy, about 2 minutes. Add salt, and mix to combine. Add flour 1 cup at a time, on medium speed, mixing until fully incorporated after each addition. Continue mixing until the dough begins to come together in large clumps.

2. Press dough about 1/4-inch thick into a 9-by-13-by-1-inch baking pan. Prick the pastry with the tines of a fork. Chill until firm, about 20 minutes. Bake until golden brown, 18 to 20 minutes. Transfer pan to a wire rack to cool completely.

3. Reduce oven to 325 degrees. To make the filling: Place butter, brown sugar, honey, granulated sugar, heavy cream, and salt in a medium saucepan over high heat. Bring to a boil, stirring constantly until mixture coats the back of a spoon, about 1 minute. Remove pan from heat; stir in nuts and vanilla.

4. Pour filling onto the cooled crust. Bake until filling bubbles, 15 to 20 minutes. Carefully transfer pan to a wire rack to cool completely. Run a paring knife around edges of the pan, and invert onto cooling rack, leaving the pastry on the rack. Invert rack with pastry onto a cutting board, leaving the pastry on the board, filling side up. Use a sharp knife to cut into 1-by-3-inch bars. Store in an airtight container up to 1 week.