Preheat the oven to 325 degrees. Butter six 4-ounce ramekins and set them in a medium baking dish. Fill a bowl with cold water and squeeze the lemon juice into it. Working with 1 artichoke at a time, snap off the outer leaves and trim off all but 1 inch of the stem. Cut off the remaining leaves at the top of the heart and peel the base and stem. Halve the artichoke and scoop out the furry choke. Add the heart to the lemon water and repeat.

In a saucepan of boiling water, cook the artichokes until tender, 10 minutes; drain and transfer to a food processor. Add 2 tablespoons of the cream; puree until smooth. Press the puree through a fine-mesh sieve into a bowl. Whisk in the remaining cream along with the eggs and season with 1/2 teaspoon of salt and a pinch of white pepper.

Pour the custard into the ramekins. Fill the dish with enough boiling water to reach halfway up the sides of the ramekins. Bake the custards for 45 minutes, until a knife inserted in the centers comes out clean. Remove the ramekins from the water.

Meanwhile, in a small saucepan of boiling water, cook the fava beans for 5 minutes. Drain, reserving 1/4 cup of the water. Transfer the favas and the reserved water to a food processor and puree until smooth.

In a skillet, heat the oil. Add the garlic, sage, and rosemary and cook over moderate heat for 1 minute. Add the tomato and cook, stirring and mashing, for 5 minutes. Add the puree and cook until heated through. Season with salt and white pepper.

Run the blade of a thin knife around each custard and invert onto plates. Spoon the sauce around the custards and serve.