Daddy's Tuna Casserole

#DADDY'S TUNA CASSEROLE
3 to 4 White POTATOES, peeled and cut into thick slices
Place slices into a cooking pot and just cover with water and a pinch of SALT. Bring to a boil and cook for about 10 minutes or until just done. Dip out the potatoes with a slotted spoon to cover the bottom of a casserole dish to RESERVE THE POTATO COOKING LIQUID to make a WHITE SAUCE:
1 to 1-1/2 cups of RESERVED POTATO COOKING LIQUID
Fresh Ground PEPPER to taste
1/2 teaspoon DRIED PARSLEY
1/4 teaspoon CAVENDAR'S GREEK Seasoning (contains OREGANO, GARLIC and ONION POWDER)
1 teaspoon LEMON ZEST
Juice of 1 LEMON
Add 2 generous TABLESPOONS of ALL PURPOSE FLOUR to 1/4 cup COLD water and stir with a whisk to make a SLURRY. Pour into the potato cooking liquid pot while whisking. (this prevents the flour from clumping).
Stir all together and bring to a boil. Continue stirring for 1 to 2 minutes while cooking to thicken the sauce. Turn off the heat and set aside.
In a casserole dish Layer the following:
Cooked Slices of POTATOES (bottom layer)
Canned TUNA in water, drained (spread on top of the potatoes with a fork)
Canned ENGLISH PEAS (I use LESUEUR), Drained (spread on top of the tuna)
Pour the WHITE SAUCE on top of these 3 layers just until covered and enough to reach the bottom potato layer.
Cover the top of the casserole with VELVEETA SLICES (final top layer)
Bake covered at 375 degrees F until bubbly (about 25 minutes) then uncover and bake an additional 5 minutes to let the cheese toast a bit (optional)
NOTE: I didn't give amounts of the Tuna, peas and cheese because it depends on how big of a casserole you want to make. My casserole is about a 9 x 11. My Daddy always made a tuna casserole twice that big.