Classes and online courses
Courses in food tech, nutrition or cookery can help to build a portfolio showing your commitment to the subject, whether they are carried out online or face-to-face. There are plenty of self-directed courses available online, eg free online courses in Food and Nutrition on Alison.com .
Distance Learning Accredited Level 2 NCFE qualification in Creative Craft Cookery. Offered by Technology Triumphs, an organisation which has been providing classes for home-educated children in Kent and has now expanded to distance learning. Assessment is by portfolio evidenced by photos.
Note that GCSE alternatives may not count as a GCSE for college entrance requirements, so be cautious if you're considering paying for a course. It's entirely up to each college. Courses can be good experience and an excellent way to show that you've shown sustained interest in the subject and are capable of starting at a higher level, but if a college says they want 4 GCSEs for you to get on a course - they generally require GCSEs or IGCSEs. They may consider an accredited Level 1 or Level 2 qualification towards their GCSE requirements, but it's important that you check this first.
Building a Food Tech Portfolio
Plan your own menus and cook the dishes. Take photos. Write up what you did. You could follow the format of the GCSE Food Preparation and Nutrition project from AQA, for example. This gives you a portfolio which you can show to college tutors to demonstrate your commitment to the subject.
College at 14-16
Some colleges accept 14-16 year-olds to study vocational subjects, which may include catering or food tech. What's available varies by area, but it can include:
Part-time classes for home-educated teenagers
Any Further Education college can accept home-ed teenagers to fill empty places in its classes part-time, but many aren't aware of this. See College for details. Once you've read this, you could contact the catering department of your local college and ask to speak to the course tutors. If they are prepared to accept your child on to the course part-time, you can then approach the administrative department with the funding information on the page above.
Full-time college at 14-16
A small number of Further Education colleges nationwide offer a full-time course for 14-16 year-olds who would otherwise be at school. Colleges have to meet certain conditions to be allowed to do this and it is a major undertaking for them. You can read more about the differences between this scheme and the home-ed part-time scheme on the College page. A list of the colleges which currently offer 14-16 recruitment is available via the Department for Education.
Apprenticeships are strictly for ages 16+ and there are many available in catering, with large chain firms more likely to offer a structured education and career path. Some catering employers offer a full range of apprenticeships all the way up to a degree apprenticeship - read about them on the Apprenticeships page.
Some colleges offer 'pre-apprenticeship' courses, which are intended to build up skills for people who want to be apprentices but aren't ready for a job yet. These are usually aimed at ages 16+.