Tomatoes Glazed With Balsamic Vinegar

1 1/2 lb. ripe but firm tomatoes
1 plump shallot, finely diced or red onion
2 tbs. butter
salt & pepper
3 tbs. balsamic vinegar
Core and wedge tomatoes about 1 1/2 in. across the widest.
In a wide skillet, large enough to hold tomatoes in a single layer;
Heat butter til it foams. Add tomatoes, saute over high heat,
turning them over several times til they begin to look dull.
About 3 min.
Add vinegar & shallot & shake pan back & forth til vinegar
has reduced leaving a thick dark sauce.
Season with plenty of salt & pepper.