Make the mustard sauce. Mix together creme fraiche with stone-ground mustard. Set aside.
Prepare the batter for the french toast. Mix together milk with garlic powder, black pepper, eggs, and grated parmesan. Dip the challah bread slices in the batter and let it sit for 10 seconds.
Melt 1 tablespoon butter in a griddle or nonstick pan over medium-low heat. Cook the french toast until golden brown, flip, and cook on the other side. Add additional butter as needed. Repeat with the remaining bread.
Top the french toast with slices of smoked salmon, capers, thinly sliced red onion, poached eggs, fresh dill, and a dollop of the mustard creme fraiche. Season with salt and pepper. Serve immediately.
Notes
The toppings including the mustard creme, sliced onions, and picked dill can be prepared ahead of time. If making a large batch of french toast, keep them warm in the oven at 200 degrees F until ready to serve.