If using a gel-canister ice-cream maker, freeze canister overnight.
Stir together 1/4 cup of the sugar and lemon zest in small bowl to evenly distribute zest. Stir in juice; set aside.
Place a large bowl and strainer on heatproof surface near stove. Combine milk and yolks in a heavy, nonstick, medium-size saucepan. Stir in remaining 1 cup sugar. Cook over medium-low heat, stirring constantly with rubber scraper, until instant-read thermometer just reaches 190 degree F, about 15 to 20 minutes (do not let mixture boil), or until slightly thickened. Strain immediately into bowl; stir in salt.
Add lemon mixture to bowl, stirring until sugar dissolves. Place wax paper directly on custard and refrigerate until chilled, about 4 hours.
To freeze, add cream to custard, stirring just to combine. Pour into ice- cream maker; process 30 minutes as per manufacturers directions.
Scrape into a 1-1/2-quart container; freeze to firm completely, about 2 hours.
Makes 8 servings.