Culinary Brulee' torch for melting the cheese or broil in oven
Melt butter and olive oil together in a stockpot over medium heat; saute onion and garlic until onion, carrots, parsnips, and celery is slightly softened, about 5-8 minutes. Add flour, rye seed, tarragon leaves, and black pepper to onion mixture; cook and stir until flour is dissolved and fragrant, about 3 minutes.
Pour chicken broth over onion mixture and stir until blended, 2 to 3 minutes. Add cabbage and corned beef; cook, stirring frequently, until cabbage is tender, about 20 minutes. Add heavy cream and cook just until liquid is warm but not boiling, about 5 minutes.
Melt cream cheese over low heat in a saucepan until creamy, 2 to 3 minutes. Whisk cornstarch and water together in a bowl; stir into cream cheese until smooth. Stir cream cheese mixture into soup; cook over low heat, stirring constantly, until cheese melts and soup is thickened, about 5 minutes. Place in bowl top with croutons, Dubliner cheese and torch until bubbly.