Blanch the spinach in boiling water. Drain on paper towels.
Butter an 8- to 9-cup (2- to 2.3-L) baking dish. Place a layer of bread slices on the bottom of the dish. Cover with all of the salmon. Sprinkle the dill over the salmon. Spread all the chèvre on enough bread slices to cover the salmon, and add to the baking dish, cheese side up. Layer the spinach evenly over the bread slices that have been spread with the cheese. Cut the remaining bread into 1-inch (2.5-cm) cubes and toss over the spinach, covering it completely. Note: The strata can be prepared to this point up to 12 hours before serving. Keep in the refrigerator, tightly covered.
Mix the milk, cream, eggs, and salt and pepper together and gently pour over the strata. Cover with plastic wrap and press down so that all the bread soaks up the liquid. Leave for at least half an hour.
Preheat the oven to 350°C (175°F).
Cook for 50 minutes to 1 hour. Remove from the oven and let the strata sit for 10 minutes before cutting into pieces. Serve with Mustard-Yogurt Sauce (see below).
Mustard-Yogurt Sauce
1 cup (240 mL) 4% yogurt or sour cream
1 Tbsp. (15 mL) Dijon mustard
Combine the yogurt or sour cream with the mustard and blend. Serve at room temperature.
Photo by Chris Freeland.