1. Blend tomatoes, Worcestershire sauce, hot sauce, lemon juice, and celery in a blender until smooth. Transfer tomato puree to a small saucepan, and season with salt.

2. Cook over medium heat, stirring occasionally, until puree is reduced slightly, about 8 minutes.

3. Pass through a fine sieve set over a bowl, pressing on solids to extract liquid; discard solids. Stir in the horseradish. (If not serving immediately, refrigerate in an airtight container up to 1 day.) Just before serving, garnish sauce with celery leaves, if desired.