Place the cream cheese and granulated sugar in the bowl of a stand mixer fitted with a paddle attachment. Or use a large bowl and a hand mixer.
Beat the cream cheese and sugar for a couple minutes to combine then scrape down the bowl and mix again for a minute. You don't want to add a lot of air so don't mix for more than about 3 minutes.
Add the eggs one at a time mixing until each is fully incorporated.
Add the vanilla and salt and mix until combined. Scrape down the bowl.
With the mixer on low add in the key lime juice and mix until combined.
Add in the flour and mix well. Scrape down the bowl.
Remove the bowl from the stand mixer and fold in the lime zest.
Pour the filling into the baked crust and smooth it out, tap it on the counter a couple times to remove any large air bubbles.
Place it in the oven on the middle rack and bake for 20-25 minutes until set but still a little jiggly.
Open the oven door slightly and allow the cheesecake to cool in there for about 20-30 minutes.
Remove from the oven and cool on a rack to room temperature.
Once cooled to room temperature place it in the fridge uncovered to cool completely - at least 2 hours up to over night.
Once cooled completely use the over hang of parchment or foil to remove the slab from the pan. Cut into 12 equal pieces (or 24 if you prefer smaller bites).
Melt the remains 2 oz of chocolate from the bar and place it in a piping bag or a zip top bag and cut a small hole in the corner.
Drizzle the cut bas with a the chocolate and serve - serve with whipped cream if you like.