Preheat oven to 375 degrees. Line an 8x8 baking pan with parchment paper and set aside.
In a bowl, cream together butter and sugar. Add vanilla and stir to combine. Add flour to butter mixture and mix until a dough forms. Dough may be crumbly, but will hold together when pinched between two fingers.
Press dough into an even layer in a lined 8x8 square baking pan. Prick the top of the dough with a fork, then bake for 20 minutes, or until lightly browned around edges and top. Remove from oven and set aside.
In a saucepan over medium heat, add butter, sugar, and honey. Bring to a boil. Boil for 2 minutes, then add heavy cream. Boil for 1 more minute.
Remove from heat and add vanilla extract and salt. Stir to combine. Add walnuts, stir to coat.
Pour topping over shortbread crust. Bake 18-22 minutes, or until entire top is bubbly. Remove from oven and allow to cool completely before slicing (topping needs time to firm up).
Slice into 16-24 pieces (these bars are very sweet, so smaller squares or rectangles work best).
Walnuts can be substituted with your favorite nut. Cashews, peanuts, or almonds are great choices.
Bars will keep for 3-5 days at room temperature in a sealed container. If storing in the refrigerator, allow to come to room temperature before serving.
Use the spoon and level method for measuring your flour: Use a spoon to add flour to your measuring cup, then level off the top with a knife. If scooping flour using your measuring cup, this compacts flour into the cup and adds up to 25% extra flour to your recipe. For best accuracy, weigh your flour instead.