Ingredients:
4-5 heirloom tomatoes, ripe and fragrant
1/2 medium red onion
1 tbsp sour cream (or Greek-style yogurt)
Salt and pepper to taste

Preparation:

Slice your tomato into thick wedges and your onion into slivers. Add sour cream, and mix well to combine. Season with salt and pepper, and serve immediately.

[You will have, after you're done, this creamy juice left over with some onions swimming in it. I implore you not to throw that out. You know that rustic bread I was referring to? Well, save a piece and dip your bread in the juices. Trust me, you'll thank me later.]