Step 1

Preheat oven to 400 F. Arrange bread on rimmed baking sheet. Bake until pale golden, about 5- 8 minutes, then cool.

Step 2

Butter a large glass baking dish (4 quart 15 x 10-inch).

Step 3

Melt 4 tablespoons butter with the olive oil in a heavy large skillet over medium-low heat. Add potatoes. Stir to coat and arrange in single layer. Cover and cook until potatoes are almost tender, about 8 minutes. Uncover; increase heat to medium-high, and cook until potatoes are lightly browned and tender, stirring occasionally, about 8 minutes. Add shallots and sauté until soft, about 2 minutes. Remove from heat. Gently mix in bread, salmon, chives, minced dill. Transfer mixture to prepare dish.

Step 4

Whisk eggs, cream, sour cream,Dijon mustard, salt and pepper in medium bowl to blend well. Pour custard over potato mixture in dish. Let stand 15 minutes, occasionally pressing bread into custard.**

Step 5

Preheat oven to 350 F. Bake casserole, uncovered, until custard is set, about 30 - 45 minutes. Cut into squared and top with additional sour cream, capers, and dill sprigs; serve hot.