The natural sweetness of ripe tomatoes goes well with the vinegar and tarragon flavor of sauce béarnaise. Prepare a tomato purée by slicing the tomatoes in half crosswise and squeezing out the seeds. (It is not necessary to peel the tomatoes, because the purée will be strained.) Coarsely chop the seeded tomatoes and gently stew them in a small amount of olive oil. They will first release water. Continue cooking until the water has evaporated and the purée begins to thicken. Strain the purée and stir it into the sauce béarnaise. Use approximately one part strained tomato purée to three parts Sauce Béarnaise: For 2 cups (500 milliliters) Sauce Choron, use 1½ cups (375 milliliters) Sauce Béarnaise and ½ cup (125 milliliters) tomato purée (2 medium tomatoes will produce this much purée). Taste while adding the purée, because the amount of purée needed will depend on the ripeness and flavor of the tomatoes and on personal taste.