You can get the result with a single database query by using a projection:
var userWithProfilePhoto = dbContext.Users
.Where(u => u.Id == 1)
.Select(u => new
{
User = u,
ProfilePhoto = u.Photos.Where(p => p.IsProfilePhoto).FirstOrDefault()
})
.SingleOrDefault();
userWithProfilePhoto.User
and userWithProfilePhoto.ProfilePhoto
are the two entities you are looking for.