Slow cooker size: 3 to 4 quart
To make the dough, place the yeast, sugar, salt, optional dough relaxer, oil, 2/3 cup water, and 3 cups flour in a large mixing bowl. Stir the ingredients together with a wooden spoon, and then turn the dough out onto a lightly floured work surface. Knead the dough gently, adding additional water or flour to form a soft, supple ball of dough.
Use the butter to generously coat the inside of the slow cooker insert. Cover the insert and turn the slow cooker on HIGH for 5 minutes, or just until the insert feels warm to the touch, and then turn it off. Place the dough in the insert and cover. Allow it to rise until doubled in bulk.
While the dough is rising, toss the filling ingredients together with a fork in a medium mixing bowl. Set aside.
When the dough has doubled in bulk, transfer it to a lightly floured work surface. Cover the empty slow cooker and heat on HIGH for 5 minutes to rewarm the insert, and then turn it off. There should still be a coating of butter on the sides of the insert. If not, coat it with more butter.
Use a rolling pin to roll the dough into a rectangle about 24 inches long and 8 inches wide. Scatter the filling mixture over the surface. Start with a long edge and roll the dough, jelly-roll style, to form a 24-inch-long roll. Try not to stretch the dough as you roll. Curl the roll into a tight spiral and place it in the warmed slow cooker insert. Cover the slow cooker and allow the dough to rise until almost doubled in bulk.
Preheat the oven to 350°F with a rack in the lower third, but not lowest position. (To accommodate the insert, you may have to remove the other shelves.) Place the insert, uncovered, in the oven and bake for 40 to 45 minutes, until the crust is well browned and an instant-read thermometer inserted in the center of the rolls registers 200°F.
While the loaf is baking, make the topping. Put the confectioners’ sugar, butter, 3 tablespoons of water, and vanilla extract in a small bowl and stir with a fork until smooth. Add just enough water, if necessary, so that the topping flows slowly off the fork.
When the loaf is done, remove the insert from the oven and immediately invert the contents onto a wire rack. Immediately, invert the loaf again onto a serving plate and spoon the topping over it. Cut the loaf into wedges and serve warm or at room temperature.