For the ricotta cheese, stack 4 large squares of cheesecloth in a colander, leaving overhang.
Combine milk and buttermilk in a large, heavy pot. Place pot over high heat. Stir almost constantly as mixture heats and curd begins to form. When temperature registers 175-180 degreees F curds will separate from the whey and float to the top. Turn off heat.
Using a slotted spoon, transfer the curds to the prepared colander. Gather cheesecloth and press gently. Do not remove too much liquid or the ricotta will be dry. Let rest in colander 15 minutes.
Transfer ricotta to a storage container. Sprinkle with a little salt and stir. Cover and chill for about 2 hours. Can be made 1-day ahead, keep chilled.
For the toast, spread homemade ricotta cheese on toast. Spread jam over ricotta cheese and sprinkle pistachios on top.