To make the pastry, put the flour in a mixing bowl. Add the butter and salt and rub gently with your fingertips until the mixture resembles fine breadcrumbs. Stir through the herbs, lemon zest and Cheddar.
Beat the egg yolk with 1 tablespoon of cold water in a bowl. Add to the flour mixture and combine until it forms a dough, adding more cold water if needed. Wrap in cling film and place in the fridge while you make the filling.
To make the filling, put the garlic in a saucepan, cover with cold water and bring to a gentle simmer. Cook for 2–3 minutes, then drain.
Wipe the saucepan dry. Add the garlic and 1 tablespoon of olive oil and fry over a high heat for 2 minutes. Add the vinegar and 100ml/3½fl oz water, bring to the boil and simmer gently for 10 minutes.
Add the honey, most of the rosemary and thyme (reserving the rest, with the sage) and a good pinch of salt. Cook over a medium heat for 5 minutes, or until most of the liquid has evaporated and the garlic is coated in a dark syrup.
Meanwhile, put the celeriac in a saucepan, cover with freshly boiled water and boil for 7–10 minutes, or until soft and slightly translucent. Drain and tip into a big mixing bowl.
Add the cheeses, crème fraiche, lemon juice, mustard, parsley, Worcestershire sauce and eggs. Add a good pinch of salt and grind of pepper and gently fold in the garlic.
Preheat the oven to 200C/180C Fan/Gas 6.
Sprinkle flour onto a clean work surface and roll out the pastry to 3-4mm thick. Line a 20cm/8in round cake tin with the pastry, ensuring a little spills over the edges. Pour the filling into the pastry case. Coarsely grate the reserved celeriac and pile it on top. Finish with the reserved rosemary, thyme, sage and a drizzle of olive oil.
Bake for 45 minutes, or until the tart filling has set and the top is golden brown. Leave to cool a little, then take it out of the tin. Serve warm with a few herbs sprinkled over.