Tonnato Sauce

2 oz (60 g) Italian canned tuna in olive oil, ½ oz (15 g) best-quality anchovy filets, ½ fl oz (15 mL) fresh lemon juice, 2 tsp (10 mL) minced lemon zest, 2 tsp (10 mL) nonpareil capers (all puréed in a mortar or food processor), 3–4 fl oz (90–120 mL) cool veal stock or veal cuisson (enough to achieve a pourable consistency)