Preheat the grill to high.
Place the speck or proscuitto onto a baking sheet and place under the grill for 3-4 minutes, or until crisp. Remove speck and place on a plate lined with kitchen paper to drain.
Cut both chicken breasts through the middle, without cutting through, to form one large flat piece. Season, to taste, with salt and black pepper and brush with olive oil.
Heat a griddle pan until hot then place the chicken breasts on it and cook for 2-3 minutes on each side, or until just cooked through.
Heat a frying pan until hot and add the butter and then the cubed bread. Fry until golden brown, then remove.
Separate the leaves from the lettuce and cut into chunky pieces.
For the dressing, in a medium saucepan, bring the garlic and wine to a boil and simmer for about 5 minutes, until the garlic has softened. Leave to cool.
Combine the wine and garlic with the egg yolks, anchovy and cheese in a mixing bowl. Blend with a hand blender or food processor until smooth. Drizzle in the oil in a thin steady stream, taking care not to add it too quickly, otherwise it could split and curdle. Stir in the mustard and add seasoning to taste.
Add the crisp-fried speck, croutons and lettuce to the dressing and toss to combine. To serve, place salad on plate, top with chicken and pour the dressing over.