Twenty Eleven: Home Page, View full post of most recent post & Summary of the rest

after creating a child theme for Twenty Eleven, copy content.php from the Twenty Eleven theme into your child theme to edit it;

find (line 35):

    <?php if ( is_search() ) : // Only display Excerpts for Search ?>

change to:

    <?php if ( is_search() || is_paged() || $wp_query->current_post > 0 ) : // Only display Excerpts for Search, paginated pages, or any other then the first post ?>

then find this section:

    <div class="entry-content">
        <?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?>

and change to:

    <div class="entry-content">
        <?php global $more; if( $wp_query->current_post == 0 && !is_paged() ) $more = 1; ?>
        <?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentyeleven' ) ); ?>