1/4 cup white wine vinegar or champagne vinegar
1/4 cup sugar
1 small shallot
1 to 1 1/2 tablespoons poppy seeds
1/2 teaspoon salt
1/2 teaspoon ground mustard
2 teaspoons mayonnaise, optional for a creamier dressing
1/2 cup olive oil, grapeseed oil, or a mix (See Recipe Note)
Whisk the white wine vinegar and sugar until the sugar is mostly dissolved (it's okay if there is still some undissolved sugar). Peel the shallot and grate it on a microplane or the smallest holes on a box grater directly into the bowl. Add the poppy seeds, salt, and ground mustard, and whisk to combine.
Whisking the dressing steadily, pour the olive oil into the dressing in a slow stream. Continue whisking until completely combined.
Transfer to a covered container and store in the fridge for several weeks. The dressing will separate as it sits; shake to recombine before using.