Whisk 2 cups heavy cream and ¼ cup nonfat dry milk powder in medium saucepan until combined.
Cook over medium heat, stirring occasionally to prevent scorching, until cream registers 180 degrees, 5 to 7 minutes.
Off heat, stir in 3 tablespoons lemon juice (mixture will slightly thicken).
Transfer cream mixture to bowl; cover; and refrigerate until it has consistency of yogurt, 2 to 4 hours.
Line fine-mesh strainer with quadruple layer of cheesecloth and set over bowl.
Pour cream mixture into prepared strainer; cover; and refrigerate until mixture has thick, soft, spreadable consistency, 12 to 24 hours.
(If mascarpone is too thick for your liking, stir in drained whey, 1 tablespoon at a time, until it reaches desired consistency. Do not add water; mascarpone will curdle.)
Mascarpone can be refrigerated for up to 3 days.
