Keep it simple by preparing just about everything ahead of time.
Arrange rubber or plastic snakes upside down in a sheet pan and fill the pan with water. Freeze for 4 hours.
Preheat oven to 350°F. Lightly toast bread on baking sheet.
Cook potato in a small saucepan of simmering salted water until tender, about 10 minutes. Drain and let cool.
Place almonds in food processor. Squeeze garlic head from bottom to release garlic from skins into food processor. Process until smooth, about 20 seconds.
Put cooked potato in processor. Soak bread in bowl of water. Squeeze out half of water. Combine bread, oil, lemon juice, vinegar and salt in processor. Process until smooth. Transfer to a bowl and refrigerate for 2 hours or up to two days. Bring to room temperature before serving.
Remove pan from freezer and let thaw for 5 minutes. Turn block of ice out onto large, high-sided tray. The block will last for 5 to 6 hours. Wash and prep vegetables. Arrange vegetables on ice. Serve with dip.