Step 1Make a cut in the outer hull of each chestnut, then roast the nuts in a shallow baking pan in a 400-degree oven for 20 minutes. Remove the nuts from the oven and wrap them immediately in a damp kitchen towel. Steam for 15 minutes, then peel.
Step 2Heat a 12-inch skillet or cast-iron casserole over medium heat and add 2 tablespoons olive oil and 1 teaspoon butter. Add the garlic clove and cook until fragrant, about 2 minutes. Add the chestnuts, carrots, turnips, onions, celery and Swiss chard ribs, and cook for 4 minutes. Season lightly with salt and pepper.
Step 3Add one-fourth cup stock and cook, stirring frequently, until the vegetables are lightly browned but still firm, about 8 to 10 minutes. Add more stock to the pan as it evaporates, about one-fourth cup each time, enough to just moisten the vegetables and cover the bottom of the pan.
Step 4Add the Swiss chard leaves, snow peas, one-fourth cup stock, 1 tablespoon olive oil and 2 tablespoons butter. Stir to combine. Cook, adding more stock only as needed until all the ingredients are meltingly tender, about 7 to 8 minutes.
Step 5Remove from heat and squeeze in the lemon juice. Adjust the seasoning, stir well and serve.