Instructions: Preheat oven to 325°. Butter the bottom and sides of a 9- by 3-inch round cake pan. If the ricotta has any standing liquid, pour it off, but you do not need to drain the ricotta. Fill a tea kettle with water, bring to a boil, and keep it hot while you prepare the batter.

In an electric mixer, beat the ricotta, cream cheese and sugar until smooth and light, scraping down the sides of the mixer once or twice. Add the sour cream or creme fraiche, lemon juice, vanilla and salt and blend well. Add the eggs one at a time; incorporate them well but do not over mix.

Pour the batter into the prepared pan. Tap the bottom of the pan against the counter to release any air bubbles. Set the pan in a larger pan or baking dish and add hot water to come halfway up the sides of the cake pan. Bake until the center is set (you can tell by jiggling the pan gently), about 2 1/2 hours. Remove from the oven but let the cheesecake cool in the water bath.

For the topping: Preheat oven to 325°. Combine the softened butter, flour, brown sugar and salt in a food processor or electric mixer with the paddle attachment and blend until the mixture clumps together like a crumbly dough. Chill for at least 1 hour. Crumble onto a baking sheet and bake the topping until golden brown, about 25 minutes. Cool completely. The topping will harden as it cools. Put the topping in a plastic bag and pound with a rolling pin to crumble it fine.

To remove the cheesecake from the pan, chill in the freezer for about 2 hours. Remove from the freezer and put the bottom of a 9-inch springform pan, or a cardboard round cut to fit, on top of the cheesecake. Dip the bottom of the pan briefly in hot water, then invert the cheesecake onto the springform or cardboard round. You may need to shake the pan gently to get the cheesecake to release.

Sprinkle the topping over the surface. Cut into thin wedges to serve.

Per serving: 390 calories, 10 g protein, 26 g carbohydrate, 28 g fat (17 g saturated), 150 mg cholesterol, 356 mg sodium, 0 fiber.