Peel vegetable marrow. Cut marrow in half; scrape out seeds and membrane. Cut into 3/4 inch (2 cm) cubes. Layer cubes with pickling salt in a large glass or stainless steel container. Let stand 2 to 4 hours. Drain well. Blanch onions in boiling water; drain and peel.

Place 6 clean 500 ml mason jars on a rack in a boiling water canner. Cover jars with water and heat to a simmer (180°F/82°C). Set screw bands aside. Keep jars hot until ready to use. Preheating Bernardin® lids is not advised.

The sealing compound used for our home canning lids performs better at room temperature than it does pre-heated in simmering water (180°F). Simply wash lids in hot, soapy water, dry, and set aside until needed.

Preheating can lead to less vacuum being achieved during water bath canning, and to buckle failures during pressure canning. In a large stainless steel saucepan, combine sugar, flour, mustard and celery seeds and turmeric. Gradually blend in water.

Add vinegar and red pepper and bring to a boil, stirring constantly. Cook until thickened, about 5 minutes. Add drained vegetable marrow and onions; return to a full boil. Remove from heat. Ladle vegetable mixture into a hot jar to within 1/2 inch (1 cm) of top of jar (headspace).

Using nonmetallic utensil, remove air bubbles and adjust headspace, if required, by adding more vegetables. Wipe jar rim removing any food residue. Centre hot sealing disc on clean jar rim. Screw band down until resistance is met, then increase to fingertip tight.

Return filled jar to rack in canner. Repeat for remaining vegetables. When canner is filled, ensure that all jars are covered by at least one inch (2.5 cm) of water. Cover canner and bring water to full rolling boil before starting to count processing time.

At altitudes up to 1000 ft (305 m), process -boil filled jars - 15 minutes.* When processing time is complete, remove canner lid, wait 5 minutes, then remove jars without tilting and place them upright on a protected work surface. Cool upright, undisturbed 24 hours; DO NOT RETIGHTEN screw bands.

After cooling check jar seals. Sealed discs curve downward and do not move when pressed. Remove screw bands; wipe and dry bands and jars. Store screw bands separately or replace loosely on jars, as desired. Label and store jars in a cool, dark place.

For best quality, use home canned foods within one year.

Processing: At altitudes up to 1000 ft (305 m), process -boil filled jars - 15 minutes - 15 minutes.

Altitude-adjusted processing table: At altitudes up to 1000 ft (305 m), process -boil filled jars - 15 minutes