To prepare the tomato concassé, first blanch the tomato to remove the skin. Cut the tomato into 4 quarters and remove the pulp and seeds. Gently flatten the tomato and carefully with your knife, trim the pulpy edge so it is one even piece. Next, dice the tomato into even-sized cubes. Set the concassé aside.

Finely mince the shallots and finely slice the chives. Cut the cold butter into tablespoon-size pieces. Slice the lemon in half, gather the white wine and set aside.

To prepare the beurre blanc, place a small saucepan over medium heat. Add the shallots and the wine. Bring to a simmer and reduce the liquid by about two-thirds until it reaches a syrupy consistency.

Turn the heat to the lowest setting and whisk in the cold butter one piece at a time to slowly form the emulsion.

Once all of the butter has been incorporated, season with salt and pepper. You may want to add a few drops of lemon juice to brighten the flavor of the sauce.

Monitor the sauce closely if you have other tasks to do before serving. Keep the sauce warm to the touch and whisk often to prevent it from splitting. You may need to turn the heat off and on to keep it at the correct temperature. The heat does not always need to be on, as the residual heat from the pan will keep it warm.

Just before serving, gently stir the tomato concassé and chives into the sauce. Pour over fish, chicken or seafood and enjoy.