For the chicken liver pâté: Melt 2 tablespoons of the butter in a large skillet over medium heat. Add the yellow onions and garlic and cook until softened, 5 minutes. Stir in the coriander, pepper, allspice and some salt.
Increase the heat to medium high and add the chicken livers. Cook, stirring occasionally, until golden brown on the outside but still pink inside, about 3 minutes. Add the heavy cream. Transfer the mixture to a food processor and puree until smooth.
With the motor running, add the remaining 7 tablespoons butter in three batches and process until fully incorporated. Add the brandy and pulse to incorporate. Season with salt.
Transfer the pâté to a bowl, cover, and refrigerate until firm, at least 3 hours and up to overnight.
For the red onion jam: Heat the olive oil in a medium skillet over medium heat. Add the red onions, thyme and 1/4 teaspoon salt. Cook, stirring occasionally, until softened, about 8 minutes.
Add the wine and simmer, stirring occasionally, until most of the wine has evaporated, about 10 minutes. Add the vinegar and sugar and cook, stirring often, until the onions are very tender and the liquid is syrupy, 3 to 4 more minutes.
Cool the jam to room temperature, and then refrigerate until ready to serve. Serve warm or room temperature
To serve, spread baguette slices with pâté and top with red onion jam.