2 kgJerusalem artichokes, unpeeled, halved lengthways350 gmgolden shallots (about 20), halved lengthways2garlic heads, halved horizontally¼ cup (firmly packed)sage6thyme sprigsFinelygrated rind and juice of 1 lemon60 ml (¼ cup)olive oil2 litres (8 cups)chicken stock1floury potato, such as pontiac, coarsely chopped2 tbspsherry vinegar, or to tasteCrisp sage and Jerusalem artichokes60 ml (¼ cup)olive oil¼ cup (loosely packed)sage4Jerusalem artichokes, cut lengthways into thin wedges
Preheat oven to 180C. Combine Jerusalem artichoke, shallot, garlic, herbs, lemon rind and juice in a large bowl, season to taste and mix to combine. Add oil, mix to coat, then spread mixture on oven trays lined with baking paper. Roast, turning occasionally, until golden brown and very tender (35-40 minutes). When cool enough to handle, squeeze garlic from skins (discard skins), then transfer mixture to a large saucepan.
Add stock and potato to pan, bring to the simmer over medium-high heat and cook until potato is falling apart (12-15 minutes). Remove thyme, process with a hand-held blender until very smooth, then pass through a sieve into a clean pan (discard solids). Add sherry vinegar, season to taste, keep warm.
For crisp sage and Jerusalem artichokes, heat oil in a frying pan over medium-high heat, add sage and cook until crisp (1 minute), remove with a slotted spoon and drain on absorbent paper. Add Jerusalem artichokes to pan, cook, turning occasionally, until golden and tender (4-5 minutes), remove with a slotted spoon, drain on absorbent paper, season to taste.
Serve soup hot, topped with crisp sage and Jerusalem artichokes.