How to Make It
Put the ricotta in a fine sieve set over a bowl. Cover with plastic wrap and refrigerate overnight. Discard the liquid in the bowl. Wipe out the bowl, add the thickened ricotta and stir in 1 tablespoon of the olive oil and season with salt and pepper.
Preheat a grill pan. Lightly brush both sides of the bread slices with oil and grill, turning once, until toasted, about 3 minutes. Transfer the toasts to a platter and rub them with the whole garlic clove.
In a small bowl, toss the red onion with 2 tablespoons of the balsamic vinegar and let stand for 10 minutes; drain the onion, discarding the vinegar. Meanwhile, in a small saucepan, boil the remaining 1/4 cup of balsamic vinegar until reduced to 1 tablespoon, about 5 minutes.
In a medium skillet, combine the remaining 2 tablespoons of oil with the minced garlic, chorizo, tarragon and parsley. Cook over low heat, stirring occasionally, just until warmed through, about 5 minutes.
Spread the ricotta on the toasts and top with the warm chorizo. Garnish with the frisée and pickled onions. Drizzle with the reduced balsamic vinegar and serve.