Wash and dry your tomato first. Ripe, firm tomatoes are best for this. Overly ripe tomatoes can also be cored, but they will be more watery and may lose their shape as they are chopped.

Using a sharp paring knife, insert a very sharp knife into the top of the tomato then gently push the knife down about 1/2 inch and using a circular motion angled into the tomato, cut around the hard core of the tomato. Once you've gone all the way around the tomato, use the tip of your knife to life the tomato core top out.

If you want to keep the seeds in your recipe, then slice and use the tomato as desired. Or, remove the seed part with a sharp paring knife, then slice and chop as desired.