Add butter for cake to a pan and start browning it over medium-low heat. In a spice grinder, grind 1/4 cup erythritol into a powder.

Add all dry ingredients to a bowl and mix together well.

In a seperate bowl, add all wet ingredients into a bowl and mix. Once butter is browned, drizzle into the wet ingredients while mixing.

Slowly add dry ingredients into wet ingredients, mixing well until a dough forms.

Press dough into a greased round cake pan and bake for 20-25 minutes at 350F.

Remove from the oven, cool, and set on a cooling rack.

Powder 1/2 cup erythritol in a spice grinder and set aside. Puree the blackberries in a spice grinder or food processor and strain off the excess seeds.

Add lemon juice and powdered erythritol into blackberry puree and mix well.

Cream 6 tbsp. butter and heavy cream together, then slowly drizzle the blackberry puree into this until a thick icing has formed.

Ice the cake and set in the fridge for 20-30 minutes.