In a 3 to 4-quart pan over medium heat, combine milk, half-and-half, and sugar. Stir often until sugar dissolves. In a bowl, beat yolks to blend. Whisk some milk mixture into yolks, then stir mixture back into pan. Stir over medium heat until mixture is thick enough to coat a metal spoon in a smooth layer, about 20 minutes. At once, set pan in ice water. Add vanilla; stir often until mixture is cool. Lift from water, cover, and chill until cold, at least 4 hours or up to 1 day. Peel peaches (see TIPS), pit, and slice. Whirl fruit in a blender or food processor with sour cream and lemon juice until smoothly pureed; add to milk mixture. Freeze according to manufacturers directions in a self-refrigerated ice cream maker, or in an electric or manual ice cream maker with 1 part salt to 6 parts ice, until the dasher is hard to turn. Serve, or freeze in an airtight container up to 1 week. Makes about 2 quarts. Per 1/2 cup: 136 cal. (30 percent from fat); 2.4 g protein; 4.5 g fat (2.4 g sat.); 23 g carbo.; 27 mg sodium; 49 mg chol. DESS 157