The prince casts an eye over Herdwick sheep
He tasted the burger, which is made from Herdwick sheep, at the Flock Tearoom in Rosthwaite, the heart of the Lake District.
The prince - a strong supporter of the countryside - is meeting tenant farmers and is holding private meetings with others, including members of the local business community.
Before going into the tearoom, he went through bio-security measures and was shown three Herdwick rams.
Hazel Relph, 44, who owns and runs the tearooms with her husband Joe, said: "He had a Herdi burger which was pure Herdwick mince and then made into burgers.
"Then he took a bite from a Herdwick and apricot sausage roll."
During a 40-minute meeting the prince spoke to local farmers about the devastation caused by foot-and-mouth in the county over the last eight months.
In that time, it has seen more than 890 cases of the disease from a national total of 2,026.
There are fears that tourism will be damaged this year by a combination of foot-and-mouth disease and the US terror attacks.
Farming 'in trouble'
Mrs Relph said they had had to close their bed and breakfast and the tearooms for six months.
She said: "It has been hard but it is still very hard. Farming is in serious trouble but it's not just foot-and-mouth.
Also at the meeting with the prince was Will Cockbain, 42, deputy county chairman of the National Farmers' Union for Cumbria.
Mr Cockbain, who farms in Keswick, said: "The prince showed a remarkable grasp of the problems that we have encountered.
"He certainly got a better understanding of some of the farming problems than, dare I say, the politicians."
'Deep concerns'
Oliver Maurice, regional director for North West Region National Trust, said after the meeting: "He was extremely well informed.
"I was very impressed by his obvious deep concerns for our farming tenants and the problems they have been suffering."
Of the 12 farmers who spoke to the prince, four have lost all of their sheep, slaughtered during the height of the disease.
Charles has been directly affected by foot-and-mouth with his Home Farm property, near his home in Highgrove, Glos, being placed under bio-security measures along with many others across the country as part of the campaign to fight the virus.
Charity donation
He has also given £500,000 to five charities who support farmers.
The prince left by helicopter to visit Cockermouth where he was to have another meeting with local farmers and local business people.
Earlier, he opened the newly restored Blackwell House, a turn of the 20th Century building at Windermere, which has become an arts and crafts gallery.