Using a recipe dating from 1714 for an “extraordinary plumb” cake, she has turned out a 2ft creation which is the weight of a small child to celebrate a market town’s golden era.
A nine-day festival in Beverley this month will mark the 300th anniversary of its Market Cross and succession of George 1, the monarch who ushered in the Georgian era, with 25 events including a masked banquet and harpsichord music by candlelight.
Mrs Mathieson’s cake - this one will feed 300 - will be handed out on the last day, after the proclamation of the King’s succession is read out by the Market Cross and a volley has been fired by “redcoats”.
The Georgian era, Mrs Mathieson says, was the start of cake-making - the first time people other than Royalty would experience one, but only as a rare treat.
Sticking to the spirit of the 1714 recipe down to her hand-made dress, which has cable ties for stays instead of whalebone, she mixed the dough by hand.
That was left for an hour to rise before being piled into a hoop of brown paper and baked for two hours in the only local oven big enough at the Darby and Joan Hall in Cottingham.
Half an ounce of nutmeg, mace and cloves combined with seven pounds of flour and currants and two-and-a-half of butter, but just 1lb of sugar, gives it a taste similar to a hot-cross bun - without the sugar hit.
Its waves of white icing are smoothed into place by a goosefeather - much easier than a spatula, said Mrs Mathieson, who added: “Early cakes were basically bread dough, with added fruit and spices, a special treat, the sort of thing that may have been served up at harvest.
“Our idea of cakes and sweet things came in with the Georgians, the age of elegance and opulence.”
It was a period in which Beverley thrived, a Jane Austen world where rich county family built townhouses to come and visit, go to the horseracing, gentlemen’s clubs and theatre.
George 1 first landed in England on September 18 - by coincidence the same day as the Scottish referendum - and organisers believe they are the only town in Britain to be marking the anniversary with a festival.
Many of the events are already sold out.
Just a few tickets are left for the masked banquet at the Minster on September 19 where delicacies including the Beverley Bun - a winning recipe by local bakers Sugar and Spice, created specially for the occasion - will be served up.
The “sticky, gooey” bun created by Trish Sutherland is already selling like hotcakes and will feature in an event this Saturday at the Market Cross where 2,000 samples will be handed out to townspeople.
Some three-quarters of the listed buildings in Beverley town centre are Georgian and a highlight of the festival will be opening 15 to the public, including private houses, Lairgate Hall and Newbegin House, home of former Tory MP Walter Sweeney.
The festival has been led by Beverley Civic Society and Beverley Renaissance Partnership, with the support of community voluntary groups and the help of £8,800 Heritage Lottery Fund funding.
“One of the great things is that it has really been a community effort,” said John Bird, co-organiser with Prof Barbara English.
“It wouldn’t have been possible without the volunteers.”
The festival runs from September 13 to September 21.