In a large skillet, melt butter and olive oil. Add leeks, celery, salt, pepper, and sage. Sauté until translucent. (To clean leeks, cut each lengthwise down the middle and run under cold water, lifting up each leaf to wash out sand and grit.)
Cube wheat bread and place in a large mixing bowl. Pour in cooked vegetable mix and stock, stir gently until combined. Stuff into cleaned turkey or chicken cavity and bake accordingly, depending on size of bird.