1L (34 oz.) water
100g (3.5 oz.) dry malt extract (for high-gravity beers, use 200g / 7 oz.)
3ml (1/2 tsp.) yeast nutrient

  • bring water to the boil
  • add dme and yeast nutrient
  • return to boil and boil for 15 minutes
  • chill wort to room temperature in ice bath
  • pour wort and room-temperature yeast into sterilized flask
  • cover with foil and agitate (preferably with a stir plate) for 18-36 hours

Source: http://homebrewacademy.com/how-to-make-a-yeast-starter