I want to change the date format from September 7, 2019 to 
this format showing month and date separately.
File is this:
<?php
/** * Widget API: WP_Widget_Recent_Posts class * * @package WordPress * @subpackage Widgets * @since 4.4.0 */
/** * Core class used to implement a Recent Posts widget. * * @since 2.8.0 * * @see WP_Widget */ class WP_Widget_Recent_Posts extends WP_Widget {
/**
* Sets up a new Recent Posts widget instance.
*
* @since 2.8.0
*/
public function __construct() {
$widget_ops = array(
'classname' => 'widget_recent_entries',
'description' => __( 'Your site’s most recent Posts.' ),
'customize_selective_refresh' => true,
);
parent::__construct( 'recent-posts', __( 'Recent Posts' ), $widget_ops );
$this->alt_option_name = 'widget_recent_entries';
}
/**
* Outputs the content for the current Recent Posts widget instance.
*
* @since 2.8.0
*
* @param array $args Display arguments including 'before_title', 'after_title',
* 'before_widget', and 'after_widget'.
* @param array $instance Settings for the current Recent Posts widget instance.
*/
public function widget( $args, $instance ) {
if ( ! isset( $args['widget_id'] ) ) {
$args['widget_id'] = $this->id;
}
$title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : __( 'Recent Posts' );
/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );
$number = ( ! empty( $instance['number'] ) ) ? absint( $instance['number'] ) : 5;
if ( ! $number ) {
$number = 5;
}
$show_date = isset( $instance['show_date'] ) ? $instance['show_date'] : false;
/**
* Filters the arguments for the Recent Posts widget.
*
* @since 3.4.0
* @since 4.9.0 Added the `$instance` parameter.
*
* @see WP_Query::get_posts()
*
* @param array $args An array of arguments used to retrieve the recent posts.
* @param array $instance Array of settings for the current widget.
*/
$r = new WP_Query(
apply_filters(
'widget_posts_args',
array(
'posts_per_page' => $number,
'no_found_rows' => true,
'post_status' => 'publish',
'ignore_sticky_posts' => true,
),
$instance
)
);
if ( ! $r->have_posts() ) {
return;
}
?>
<?php echo $args['before_widget']; ?>
<?php
if ( $title ) {
echo $args['before_title'] . $title . $args['after_title'];
}
?>
<ul>
<?php foreach ( $r->posts as $recent_post ) : ?>
<?php
$post_title = get_the_title( $recent_post->ID );
$title = ( ! empty( $post_title ) ) ? $post_title : __( '(no title)' );
?>
<li>
<a href="<?php the_permalink( $recent_post->ID ); ?>"><?php echo $title; ?></a>
<?php if ( $show_date ) : ?>
<span class="post-date"><?php echo get_the_date( '', $recent_post->ID ); ?></span>
<?php endif; ?>
</li>
<?php endforeach; ?>
</ul>
<?php
echo $args['after_widget'];
}
/**
* Handles updating the settings for the current Recent Posts widget instance.
*
* @since 2.8.0
*
* @param array $new_instance New settings for this instance as input by the user via
* WP_Widget::form().
* @param array $old_instance Old settings for this instance.
* @return array Updated settings to save.
*/
public function update( $new_instance, $old_instance ) {
$instance = $old_instance;
$instance['title'] = sanitize_text_field( $new_instance['title'] );
$instance['number'] = (int) $new_instance['number'];
$instance['content'] = (int) $new_instance['content'];
$instance['show_date'] = isset( $new_instance['show_date'] ) ? (bool) $new_instance['show_date'] : false;
return $instance;
}
/**
* Outputs the settings form for the Recent Posts widget.
*
* @since 2.8.0
*
* @param array $instance Current settings.
*/
public function form( $instance ) {
$title = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
$number = isset( $instance['number'] ) ? absint( $instance['number'] ) : 5;
$show_date = isset( $instance['show_date'] ) ? (bool) $instance['show_date'] : false;
?>
<p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" /></p>
<p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of posts to show:' ); ?></label>
<input class="tiny-text" id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" /></p>
<p><input class="checkbox" type="checkbox"<?php checked( $show_date ); ?> id="<?php echo $this->get_field_id( 'show_date' ); ?>" name="<?php echo $this->get_field_name( 'show_date' ); ?>" />
<label for="<?php echo $this->get_field_id( 'show_date' ); ?>"><?php _e( 'Display post date?' ); ?></label></p>
<?php
}
}