Potato Gratin

First, let me tell you that this is the best potato dish I have ever eaten.  It is so rich and flavorful that it will definitely become a holiday staple.  Your dad and I both grew up eating scalloped potatoes made from a box which at the time was "the new way" of convenience cooking.  Thankfully, times have changed back to where cooking from scratch is much cooler and always better than from a box mix.  During the 2020 Coronavirus quarantine, we had lots of opportunities to try out new recipes, and thank goodness we tried this one!  It is an Ina Garten (my fav) classic with only a couple of minor changes.  Several prep steps are required for this gratin but believe me, it's well worth the time.

Ingredients:
4 large russet potatoes
1 large sweet onion
1 small fennel bulb (stalks removed)
2 1/2 cups Gruyere cheese, grated
2 cups plus 2 tablespoons heavy cream
salt and pepper

Preparation:
Preheat your oven to 350 and coat a 9x13 baking dish with butter.
Cut off the stalks from the fennel bulb and cut the bulb in half.  Then slice it thinly.
Cut the onion in half and also slice it very thinly.
Add butter and olive oil to a pan and heat to
medium-high.  Add fennel and onion and cook about 10-12 minutes until caramelized.
Meanwhile, peel the potatoes and slice them very thinly using a mandoline or other slicer. (this step is the most important!  The potatoes must be very thin which I personally cannot do with a knife.)
Place potatoes in a large bowl and use a few paper towels to dry up some of the liquid from the potatoes (don't stress about this step, just soak up some of the liquid and leave the rest).
Add 2 cups of the cheese and 2 cups of heavy cream to the bowl with the potatoes and season well with salt and pepper.
Add the onion and fennel to the potato mixture and mix everything together well.
Pour mixture into your baking dish and smooth it out, pressing everything down gently.
In a small bowl mix together the other 1/2 cup of cheese and 2 tablespoons of cream.
Sprinkle this all over the top of the casserole.  Note:  it will look like it is not enough but use your fingers to spread it all around and it will be perfect!
Bake for 1 hour, then cover with foil and bake another 15 minutes.
Remove from oven and make sure potatoes are soft and casserole is brown and bubbling!
Let cool 10-15 minutes.
Enjoy!