Create an object based on data from a text file

The following method reads specially formatted text (TOML) from a file and parses the input using a parser to get a few properties, which are then used to create an object.

The profiler tells me that this method is the bottleneck in my program. While parsing ~5000 files, this method eats up over 95% of the total running time. While in another method, I am able to write the data parsed from this method to a text file in under 4 seconds for more than 5000 files, this method takes around 15 seconds on an average to run.

/**
* Creates an appropriate instance of a Parsable implementation depending
* upon the header of the file.
*
* @param file the path of the file from which to create a Parsable.
* @return the created Parsable.
*/
private Parsable createParsable(Path file) {
    Toml toml = new Toml();
    try (BufferedReader br = Files.newBufferedReader(file, StandardCharsets.UTF_8)) {
        StringBuilder header = new StringBuilder();
        String line;
        while ((line = br.readLine()) != null && !line.equals(HEADER_DELIMITER)) {
        header.append(line).append("\n");
        }
        toml.parse(header.toString());
        String title = toml.getString("title");
        author = toml.getString("author") != null ? toml.getString("author") : author;
        String date = toml.getString("date");
        String slug = toml.getString("slug");
        LocalDate publishDate = LocalDate.parse(date, DateTimeFormatter.ofPattern(config.getDateFormat()));
        String layout = toml.getString("layout");
        List<String> tag = toml.getList("tags");
        StringBuilder content = new StringBuilder();
        while ((line = br.readLine()) != null) {
            content.append(line).append("\n");
        }
        if (layout.equals("post")) {
            return new Post(title, author, publishDate, file, content.toString(), slug, layout, tag);
        }
        else {
            return new Page(title, author, file, content.toString(), slug, layout, tag);
        }
    }
    catch (IOException ex) {
            Logger.getLogger(DirectoryCrawler.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

It is important to note that this method gets called over 5000 times in my test. I have tried analyzing separate parts of the method for the performance problem, but haven't been able to identify any. How can I write this better?

The TOML library is from here : https://github.com/mwanji/toml4j

And the implementation of the constructors are like so:

/**
 * Creates a Post with the given paramenter.
 *
 * @param titl the post title
 * @param auth the post author
 * @param dat the post date
 * @param loc the post's Path
 * @param cont the post's content
 * @param slu the post slug
 * @param lay the layout
 * @param tag the list of tags
 */
public Post(String titl, String auth, LocalDate dat,
            Path loc, String cont, String slu, String lay, List<String> tag) {
    title = titl;
    author = auth;
    //TODO add summary option
    //this.summary = summ;
    date = dat;
    location = loc;
    content = cont;
    slug = slu;
    layout = lay;
    tags = tag;
}