Preheat oven to 325°F/162°C.
Trace a circle around your cake pan on a sheet of parchment paper using a marker. Cut out the circle and put it in the cake pan.
Brush the cake pan and parchment paper with oil on the inside of the pan.
Bring a small pot of water to a boil. Peel and slice half a zucchini into rounds. Blanch the zucchini in the boiling water for 5 minutes. Drain the zucchini from the water and immediately blend in a food processor until smooth. Let this cool for 5 minutes before adding to the cake batter.
Sift the dry ingredients (except the sweeteners) together in a bowl and mix well with a whisk.
Mix the eggs, sweeteners, cooled zucchini puree, oil and vanilla extract together and whisk until smooth.
Whisk in the sifted dry ingredients in stages until smooth but don't overwork the batter.
Pour all of the cake batter into the greased cake pan. Bake the cake for 30-35 minutes at 325°F/162°C or until a toothpick poked in the center comes out clean. Alternatively, you can use a digital thermometer to test the inside of the cake. Once the inside reaches 200°F/94°C it's ready. While the cake bakes, make the toffee sauce. Combine the Allulose and butter in a large, shallow pan. Bring to a simmer over low heat and stir briefly with a whisk (watch carefully as allulose burns faster than sugar). Once the sweetener and butter become a medium brown colour, add the Swerve brown and whisk in. Continue cooking for 1 minute to dissolve the Swerve and then turn off the heat.Slowly add the cream to the caramel (be careful as it may splatter) and whisk until smooth. Add the vanilla extract and simmer for 1 minute to thicken the sauce.
Once the cake is ready, let it cool completely on a wire rack in the cake pan.
When the cake has cooled, poke holes in the top with a toothpick.
Pour about ⅓ of the toffee sauce over the cake and let cool for about 1 hour.
To serve, heat the sauce until warm and pour generously over a slice of the cake. Optional: garnish with a dollop of sugar-free whip cream or a scoop of keto vanilla ice cream.Enjoy!