Preheat the oven to 350° and grease a 9x13 casserole dish. Set aside.
To make the crust, melt the butter in a medium pot until it begins to foam and grow, about 5 minutes. Once it foams, stir it until you see brown speckles in the butter. Remove from heat and let it cool 2-3 minutes.
Once the butter has cooled slightly, add sugar, vanilla, and flour and stir until well combined.
Once combined, press firmly into the bottom of the casserole dish. The crust does not need to go up the side walls, just on the bottom.
Once your crust has formed, bake it uncovered 10-12 minutes. Make the filling while the crust bakes.
In the same medium pot, melt the butter, sugar, and heavy cream. Whisk and let the mixture come to a boil, then let it boil 2-3 minutes.
Crack eggs into a small mixing bowl and beat lightly, then slowly add about 3/4 cup of the boiling sugary mix while whisking aggressively. Don't add the mix all at once and make sure to stir the entire time.
Once the eggs have combined with the mix, slowly whisk it back into the pot with the rest of the filling. Add your chopped pecans and stir until they've been integrated.
Once the par-baked crust is out of the oven, spread the filling over it and once it evenly covers the crust, pop it back in the oven for 25-30 minutes. Test that the bars are done by inserting a toothpick or non-serrated knife into the middle and see if it comes back mostly clean.
Let the bars cool completely on a cooling rack about 4 hours, then cut into bars and serve.