Preheat the oven to 350 degrees. Grease or butter a 9x13 inch baking dish.
Place potatoes in a large pot and add enough salted water to cover. Bring to a boil and simmer for 10-15 minutes, until potatoes are just tender, but still firm. Rinse with cold water. Drain and set aside.
In a large sauté pan, melt the butter. Add the onion and garlic and cook until fragrant and tender, 3-5 minutes. Stir in the flour and cook a few minutes more.
Stir in the cream and milk. Bring to a simmer, stirring often, until sauce is slightly thickened and smooth. Stir in 3/4 cups of the feta 1/2 of the dill, and the parsley. Season with salt and pepper, to taste
Add the cooled potatoes to the prepared pan. Pour the cream cheese mixture over the top and sprinkle with the remaining feta.
Bake uncovered for about 20 minutes, or until the top begins to brown.
Remove from the oven and sprinkle with the remaining dill. Drizzle with a squeeze of fresh lemon juice.