Heat oven to 350°F Grease 2 9-inch round cake pans with softened butter.
Melt chocolate in double boiler. Then, combine cocoa powder and hot water and pour mixture into melted chocolate in boiler. Stir 1 minute. Add 1/2 cup malitol to chocolate mixture and stir 1 1/2 minutes.
Remove from heat.
Mix oat flour, baking soda, and salt in medium bowl.
Combine buttermilk and vanilla in small bowl.
Beat eggs and yolks on medium speed 10 seconds. Add remaining 1 1/4 cup malitol crystals increase speed to high 2-3 minutes.
Add chocolate mixture to egg/malitol mixture and mix on medium speed 30-45 seconds. Add softened butter 1 Tbsp at a time. Add 1/3 of oat flour followed by half of buttermilk mixture and mix until incorporated and alternately mix until all oat flour and buttermilk blended inches.
Pour batter into prepared cake pans.
Bake 25 minutes. Cool cake pans 20 minutes then invert on wire rack. Let cakes cool 1 hour before frosting.
Melt chocolate in double boiler. Remove from heat. Pour chocolate into medium bowl.
Gradually whisk by hand cream into melted chocolate.
With an electric mixer on medium speed, beat in butter, Malitol powder, cocoa powder, vanilla extract. Pour in chocolate mixture and beat until smooth and fluffy.
Place 1 cake layer on serving platter. Spread 1/2 cup frosting evenly across top of cake. Place second layer on top then spread remaining eve evenly on top and sides if you wish. I like to pile all my frosting on top. Cut and serve.
You can buy Malitol sugar replacer at whole food stores. For this recipe, you will need both Malitol crystals and Malitol powder. The brand I use is Nature Sweet. It measures cup for cup like sugar and is a natural sugar free sweetener made from corn. It contains no artificial ingredients and is suitable for low carb and diabetic diets. Once you cook with this, you will never want to use any other artificial sweetener again. This has no aftertaste and tastes just like sugar.