⅓cupwhole milk plain yogurt (I used 1 tablespoon cream and the rest non-fat Greek yogurt instead)
Ideal slow cooker size: 6- to 7-Quart.
Place a coil of aluminum foil or 3 metal rings from glass canning jars in the bottom of your slow cooker.
Coat a small baking pan that will fit in your slow cooker with non-stick baking spray with flour. (I used a small 6-cup Bundt pan).
In a large bowl, whisk together the flour, sugar, pumpkin pie spice, baking powder, baking soda, and salt.
Add the egg, butter, yogurt and vanilla to the flour mixture. Using an electric mixer on medium speed, beat for 1 minute, until blended. Scrape the sides and bottom of the bowl with a spatula. Beat on high speed for 2 minutes.
Spread the batter evenly into the prepared pan.
Place in the slow cooker. (I used my 6-Quart.)
Place a chopstick or wooden spoon handle at one end of the slow cooker to vent the lid. (The slow cooker should be covered but propped open a crack at one end.)
Bake on HIGH for 2 to 3 hours or until a toothpick inserted into the center of the cake comes out with a few moist crumbs attached. (My cake was done in 2 hours 15 minutes.)
Carefully remove from the slow cooker and place your baking pan on a rack to cool. Invert the cake onto a rack to cool completely. Just before serving, dust with confectioner's sugar.