Preheat oven to 350 degrees F (175 degrees C). Line a 9-inch glass baking pan with parchment paper.
Combine flour, 1/2 cup butter, white sugar, and 1/2 teaspoon salt in a bowl. Press crust mixture into the bottom of the prepared pan.
Bake in the preheated oven until crust is golden brown, about 20 minutes. Let cool.
Clip a candy thermometer to the side of a saucepan over medium-high heat. Melt 1 cup butter in the saucepan. Add brown sugar, honey, 1 1/2 teaspoon sea salt, and vanilla extract. Cook and stir until mixture reads 220 degrees F (104 degrees C) on the thermometer, 2 to 3 minutes.
Stir heavy cream slowly into the honey mixture. Add cashews. Cook, stirring occasionally, until mixture begins to harden and reads 238 degrees F (114 degrees C), 4 to 5 minutes. Pour topping over the crust. Let cool until firm to the touch, at least 1 hour. Lift out of the pan and cut into 1-inch pieces.