Allow HTML tags in the excerpt

functions.php

// Custom excerpt accepting html tags
function wpse_allowedtags() {
    // Allow the following HTML tags:
    return '<br>,<p>'; 
    }

if ( ! function_exists( 'wpse_custom_wp_trim_excerpt' ) ) : 
    function wpse_custom_wp_trim_excerpt($wpse_excerpt) {
    $raw_excerpt = $wpse_excerpt;
        if ( '' == $wpse_excerpt ) {
            $wpse_excerpt = get_the_content('');
            $wpse_excerpt = strip_shortcodes( $wpse_excerpt );
            $wpse_excerpt = apply_filters('the_content', $wpse_excerpt);
            $wpse_excerpt = str_replace(']]>', ']]&gt;', $wpse_excerpt);
            $wpse_excerpt = strip_tags($wpse_excerpt, wpse_allowedtags()); /* Keep only if you want some specific tags selected in the begining. Remove if you want all the HTML tags to be allowed */
            return $wpse_excerpt;   
        }
        return apply_filters('wpse_custom_wp_trim_excerpt', $wpse_excerpt, $raw_excerpt);
    }
endif; 

remove_filter('get_the_excerpt', 'wp_trim_excerpt');
add_filter('get_the_excerpt', 'wpse_custom_wp_trim_excerpt');