Preheat oven to 375°F.

Sprinkle chicken with 2 tsp of the salt and the pepper; tie legs together with butcher’s twine. In Dutch oven or large heavy-bottom pot, heat oil over medium heat. Place chicken breast side down and brown all over, about 5 minutes per side. Turn off heat; remove chicken to platter, reserving fat.

Heat Dutch oven over low. Add garlic and fry, stirring, until golden all over; transfer to chicken platter. Sprinkle flour over remaining fat and stir to combine.

Increase heat to medium. Pour in milk in slow, steady stream, whisking constantly until smooth; bring to a boil and remove from heat. Stir in lemon zest, sage and bay leaf; nestle chicken into pot and cover with lid.

Cook in oven for 45 minutes. Increase heat to 425°F; remove lid and, using large spoon, baste chicken with milk mixture. Return to oven and cook until skin is golden, about 15 to 20 minutes.

Remove chicken to platter; discard sage and bay leaf, and skim off liquified fat if excessive. Using immersion blender, purée milk mixture; it should be the consistency of heavy cream. (Add water to thin if needed.) Stir in lemon juice. Check seasoning and adjust if needed. Serve sauce alongside chicken.