Add the milk to a medium saucepan and place over LOW heat
Bring the milk to a very low simmer, stirring occasionally; don't let it boil (see Note 4)
Turn off the heat, but don't take the saucepan off the stove yet
Slowly pour in the vinegar or lemon juice, stirring the milk as you pour (it's going to curdle and separate right away, that's exactly what you want)
Remove the saucepan from the heat and let it stand for 10-15 minutes to cool down a little and finish curdling
Line a strainer with cheesecloth or paper towel and pour in the contents of the saucepan to drain the whey (see Note 5)
As soon as the ricotta finishes draining, transfer it to a high-powered hand blender or an immersion blender cup (my preferred method)
Add 1 tablespoon of cream and blend
Once it becomes too difficult to blend, add another tablespoon of cream and continue blending until smooth, adding more cream if necessary
Optionally add salt to taste (see Note 3)
Use the cream cheese as a spread for bagels or sandwiches, or use it in any sweet or savory recipe