Spray your slow cooker well with non-stick cooking spray.
Blend dry ingredients in a large mixing bowl (flour, baking powder, baking soda, Allspice, and salt) and set aside.
In a large mixing bowl, beat together the butter and sugar at high speed until light and fluffy, about 3 minutes.
Add eggs to the butter and sugar mixture, one at a time, blending after each.
Add the pumpkin to the sugar mixture and blend well.
Turn your mixer down to a lower speed to keep the flour from blowing up, then carefully add the flour mixture a little at a time, blending as you go. Keep adding the flour and blending until it is all incorporated into the batter.
Blend until smooth for about 2 minutes, on medium-high speed.
Now, pour the cake batter evenly into your prepared crockpot.
Cover and cook on HIGH for about 2-2 1/2 hours. Cooking times may vary depending on your slow cooker.
A toothpick inserted into the center should come out clean when your cake is done.
Carefully turn the cake out onto a large platter or cake plate. Allow your cake to cool completely before adding a topping.
This cake is delicious without a glaze, topping, or icing. I have drizzled it with my Maple Pecan Topping, and we loved it.
You may wish to line your slow cooker with aluminum foil and then spray. Slow cooker cakes tend to become well done around the edges, the foil may help prevent that.