Heat butter and margarine in a large pot or Dutch oven.

Add chopped onion, minced celery, and minced carrots and cook until softened.

In a separate bowl, mix together plain flour, gravy powder, salt, and pepper.

Add cubed beef to the flour mixture and toss to coat.

Place canned tomatoes, bay leaf, mixed dry herbs, and granulated sugar in the pot with the cooked vegetables.

Bring the mixture to a boil, then add the beef and vegetables.

Heat thoroughly and transfer to a casserole dish.

Cover and cook in the oven at 180°C (350°F) for approximately 1.5 hours, or until the beef is tender.

To make the scones, place self-raising flour, salt, and mixed dry herbs in a bowl.

Rub in margarine until the mixture resembles fine breadcrumbs.

Add low-fat milk and mix until a dough forms.

Roll the dough onto a floured surface to approximately 1cm (1/2 inch) thickness.

Cut out 12 scones using a 5cm (2-inch) plain cutter.

When the beef is tender, remove the casserole dish from the oven.

Arrange the scones in an overlapping circle around the edge of the dish.

Return the dish to the oven for 30 minutes, or until the scones are well risen and golden brown.

Serve the cobbler with potatoes, rice, or green vegetables.