Place a colander in a 2-quart glass measure or bowl. Line colander with 4 layers of cheesecloth, letting cheesecloth hang over the edge of colander. Spoon the yogurt into colander. Cover loosely with plastic wrap; refrigerate 12 hours. Spoon drained yogurt into a bowl, and set aside; discard cheesecloth and liquid.
Moisten another 3 layers of cheesecloth in wine; squeeze excess wine from cheesecloth until barely damp, reserving 2 tablespoons of wine. Line a 4-cup gelatin mold or heart-shaped cake pan with the dampened cheesecloth, letting cheesecloth hang over edge of mold, and set aside.
Combine reserved 2 tablespoons of wine, grated onion, cream cheeses, and salad dressing mix in a large bowl; beat at low speed of a mixer until smooth. Stir in drained yogurt; set aside.
Sprinkle gelatin over water in a small saucepan; let stand 1 minute. Cook over low heat, stirring until gelatin dissolves. Remove from heat; let cool slightly. Stir 2 tablespoons yogurt mixture into gelatin mixture with a wire whisk. Add gelatin mixture to remaining yogurt mixture, stirring well.
Spoon yogurt mixture into prepared mold. Fold cheesecloth over top of yogurt mixture, and chill up to 24 hours (mixture will get a rubbery texture if chilled more than 24 hours).
To serve, unfold cheesecloth, and invert mold onto a serving plate; discard cheesecloth. Garnish with fresh herbs, if desired. Serve with heart-shaped lahvosh or plain crackers.