1 rotisserie chicken
1 cup chicken stock
1 bunch broccolini, trimmed
4 tbsp. butter, plus more, softened, for the toast
1 shallot, finely chopped
1 large clove garlic, finely chopped
1 bay leaf
3 tbsp. flour
A pinch of cayenne
¼ cup dry sherry or white wine
1 ½ cups whole milk
½ cup each grated white cheddar and grated Parmigiano-Reggiano
Freshly grated or ground nutmeg
4 slices (1/2 inch thick) white bread or brioche, toasted
Finely chopped fresh flat-leaf parsley and paprika, for serving
In a large pot, bring 3 inches of water to a boil over high heat.
Pull the white meat from the chicken and tear it into large bite-size pieces, discarding the skin and bones. (Reserve the dark meat for another use.) In a large skillet, heat the chicken in the stock over medium until warm, about 2 minutes.
Salt the boiling water and add the broccolini. Cook until crisp-tender, about 5 minutes; drain.
In another skillet, melt 4 tbsp. butter over medium to medium-high heat. Add the shallot, garlic, and bay leaf and stir until the shallot and garlic soften, about a minute. Whisk in the flour and cayenne. Cook, whisking often, until the flour is absorbed, about 1 minute. Whisk in the sherry, then the milk, and bring to a bubble. Cook, stirring often, until thick enough to coat a spoon, about 3 minutes. Stir in the cheeses. Season the Mornay sauce with white pepper and nutmeg. Using a slotted spoon, transfer the chicken to the sauce. Remove the bay leaf. If the sauce is too thick, thin it with some stock from the skillet.
Butter the toast; cut corner to corner. Arrange 2 pieces on each plate. Top with the broccolini, chicken, and sauce. Garnish with parsley and paprika.