White potatoes work best for this recipe. Although they are similar in appearance to the russet (or baking potato), white potatoes, sometimes labeled "boiling" potatoes, have lighter skin and less-starchy flesh.
Lightly coat 6 (8-ounce) soufflé dishes with cooking spray. Sprinkle evenly with breadcrumbs. Set aside.
Place potatoes in a medium saucepan; cover with water. Bring to a boil. Reduce heat, and simmer for 20 minutes or until very tender; drain. Cool. Combine potatoes, buttermilk, and next 4 ingredients (through egg) in a food processor; process until smooth. Transfer potato mixture to a large bowl.
Position oven rack to lowest setting; remove middle rack. Preheat to 425°.
Melt butter in a nonstick skillet over medium-high heat. Add leek to pan; sauté 6 minutes or until tender. Add leek, cheese, and bacon to potato mixture; stir well to combine.
Place egg whites in a large mixing bowl; beat at high speed with a mixer until stiff peaks form (do not overbeat). Gently fold one-fourth of egg whites into potato mixture; gently fold in remaining egg whites. Gently spoon mixture into prepared dishes. Sharply tap dishes on counter 2 to 3 times to level. Place dishes on a baking sheet; place baking sheet on the bottom rack of a 425° oven. Immediately reduce oven temperature to 350° (do not remove soufflés from oven). Bake 40 minutes or until a wooden pick inserted in the side of soufflé comes out clean. Serve immediately.