Preheat your oven to 350°F (177°C).
In a large mixing bowl, beat together the softened butter and sugar until creamy. Add in the flour, salt, and eggs, blending until smooth. Incorporate the buttermilk, lemon juice, and vanilla extract; blend thoroughly. If the mixture appears curdled, continue to blend until it smooths out.
Pour the filling into the pre-made 9-inch deep-dish pie shell. Place the pie pan on a cookie sheet and transfer it into the preheated oven. Bake for 30 minutes.
In a medium bowl, pinch together the light brown sugar, flour, softened butter, and ground cinnamon. Add the chopped pecans and mix until a crumble forms.
After 30 minutes of baking, remove the pie from the oven and evenly distribute the pecan streusel on top.
Return the pie to the oven and continue baking for an additional 20 minutes.
Allow the pie to cool on a wire rack for approximately 30 minutes.
Fill a disposable piping bag with the salted caramel sauce. Cut the tip of the bag and drizzle the sauce evenly over the cooled pie.
Once the caramel sauce has set, the pie is ready to be sliced and served.