Place the raisins and water in a 10" Dutch oven over medium-high heat.

Let the water come to a simmer, then reduce the heat and let the raisins simmer uncovered until they turn a caramel-brown color and soften, 15 to 20 minutes.

Drain the raisins and set aside, reserving all the cooking liquid.

Measure out 1 cup of the reserved liquid and place this in the Dutch oven.

Place a rack in the center of the oven and preheat the oven to 350°F.

To the 1 cup warm liquid, add the shortening and stir to melt.

Let this cool.

Stir in the baking soda, sugar, cinnamon, nutmeg, salt, and flour until smooth.

Stir in the reserved raisins.

Set aside.

For the topping, place the remaining cooking liquid in a medium-size pan with the sugar and shortening over medium-high heat.

Bring to a boil and cook, stirring, until the mixture thickens and is syrupy, 10 to 15 minutes.

If you have a candy thermometer, bring the mixture to 220°F.

Stir well and pour carefully onto the top of the cake batter.

Cover the Dutch oven, and place the pan in the oven.

Bake the cake until it springs back when lightly pressed in the center, 25 to 30 minutes.

Serve warm.