Scalloped Potatoes with spinach

2 lbs tiny new potatoes , sliced 1/4-inch thick 1 cup chopped onion 3 garlic cloves , minced 3 tablespoons olive oil , divided 3 tablespoons all-purpose flour[...]

1 (10 3/4 ounce) can condensed cream of celery soup 1 (8 ounce) package spreadable cheese with garlic and herbs (such as Rondele) 1 1/4 cups milk 1 (16 ounce)[...]