Starters generally have an OG between 1.03 and 1.04. So if Mr. Malty says you need a 3-liter starter, you'd add between 8.3 and 11 oz of DME to 3l of water, assuming 1.046 points per pound per gallon for the DME.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: sLambic II, Flanders Red II
Primary: Fat Man Porter, Orange Blossom Mead, sLambic I
Secondary: Flanders Red I
Kegged: 3 different ciders, Janet's Brown, Barrel-aged Stout, Hallertau Blanc Pale Ale
Bottled: Flanders Red I