Melt butter in a large sauté pan over medium-high heat. Add mushrooms and sauté until tender and almost all liquid has evaporated, about 5 minutes. Add shallot, thyme and and cook 1 minute. Add brandy, stir in, then add cream. Reduce cream for a minute or 2, until thickened slightly. Season to taste.
While mushrooms are cooking, prepare crostini. Slice 6 thin slices of baguette on the bias. Spread a little butter on each slice and toast in a n oven preheated to 400F (200C) until just golden and crispy.
For pumpernickel French toast, whisk eggs with milk. Heat a griddle over medium heat. Dip each slice of bread in egg mixture to coat. Grease griddle with buter and fry French toast about 3 minutes on each side until golden. Remove from griddle and keep warm.
To serve, cut each French toast slice in half and spoon mushrooms over. Serve immediately.