Garlic Potatoes Gratin

It's been quite a  while since I made these, but I will endeavor to remember what I did. Here, however, is the recipe:

The recipe called for 3 lbs of red potatoes, 6oz Gouda,shredded, 3 tbsp butter, 5 cloves garlic, 1.5 c heavy cream, 1 tsp salt, and a 1/2 tsp pepper.

Again, I didn't have any cream. I also decided that russet potatoes were cheaper and could work just fine. I don't know how many I used and had no idea how many 3 lbs were, so I just put them into my 9x13 pan until it looked like enough. I peeled and sliced them thin (remember "gratin" = "scrapings"). I shredded.....6 oz of mozzarella? or was it monterey jack? a little of both? I shredded cheese.

I layered the pan--1/2 of the potatoes, 1/2 of the cheese, then the rest of the potatoes.
Then I sauteed the garlic and half an onion in the butter, adding flour to create a roux with 1/5 c of milk. (added salt and pepper)
I poured this over the potatoes and added the rest of the cheese.

Baked for 75 minutes at 325 degrees. For the first 30-40 minutes, cover with foil.

These were delicious, but I shouldn't have made so many. I got sick of them. Jeff really loved them, though.