Version1_Not_Working.php

<?php
    namespace Typovision\Simpleblog\Service;

    class SignalService implements \TYPO3\CMS\Core\SingletonInterface {
        public function handleInsertEvent(\TYPO3\CMS\Extbase\DomainObject\DomainObjectInterface $object, $signalInformation) {
            if($object instanceof \Typovision\Simpleblog\Domain\Model\Blog) {
                $logfile    = "C:\\xampp\\htdocs\\t3Test\\testLog.txt";
                \TYPO3\CMS\Extbase\Utility\GeneralUtility::writeFile($logfile, "test");
            }
        }
    }
?>

Version2_Working.php

<?php
    namespace Typovision\Simpleblog\Service;

    class SignalService implements \TYPO3\CMS\Core\SingletonInterface {
        public function handleInsertEvent(\TYPO3\CMS\Extbase\DomainObject\DomainObjectInterface $object, $signalInformation) {
            if($object instanceof \Typovision\Simpleblog\Domain\Model\Blog) {
                $logfile    = "C:\\xampp\\htdocs\\t3Test\\testLog.txt";
                $handle     = fopen($logfile, "a+");
                fwrite($handle, "test");
                fclose($handle);
            }
        }
    }
?>

/** File: AdditionalConfiguration.php*/
$GLOBALS['TYPO3_CONF_VARS']['LOG']['Typovision']['Simpleblog']['writerConfiguration'] = array(
        \TYPO3\CMS\Core\Log\LogLevel::DEBUG => array(
                'TYPO3\CMS\Core\Log\Writer\FileWriter' => array(
                        'logFile' => 'C:\\xampp\\htdocs\\t3Test\\testLog.txt'
                ),
        ),
);

/** File: SignalService */

/** @var \Psr\Log\LoggerInterface  $logger */
$logger = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\Log\LogManager::class)->getLogger(__CLASS__);
$logger->debug('test');