Butter a 9×9-inch baking pan, then line with a parchment paper sling and set aside.
Combine butter, granulated sugar, brown sugar and salt in the bowl of a stand mixer fitted with a paddle attachment. Cream until light and fluffy, about 3 minutes. Beat in vanilla. Add flour and slowly mix until dough begins to clump. Dump the dough into the prepared baking pan and press it down into a smooth, even layer. Chill for at least 20 minutes.
While crust is chilling, preheat oven to 350°F.
Bake crust for 20-22 minutes, or until edges are lightly browned. Set aside to cool.
In a heavy 2-quart saucepan over medium heat, melt butter and stir in sugar, corn syrup and condensed milk. Stirring to keep from scorching let mixture come to a boil and continue to cook until mixture turns a golden brown (245°F). Remove from heat, cool 15 minutes, and then stir in eggs.
Sprinkle chocolate in tart shell, cover with caramel sauce, and sprinkle nuts evenly over the top. Bake until center is set, 20-25 minutes. Cool before slicing into wedges for serving.
Melt in a large pot over high heat. Add apples, lemon juice, brown sugar, cinnamon and salt and toss to coat. Cook, stirring often, until apples are soft and the liquid has mostly evaporated, about 15 minutes.
Spread filling over the crust and crumble streusel evenly over top. Bake for 30-35 minutes, or until topping is browned. Top with small dollops of Salted Caramel Snack Spread; cool completely. Use parchment paper sling to carefully transfer bars to a large cutting board, then cut into 16 bars.