- Preheat oven to 180°C (350°F) with rack in the centre.
- Place chocolate in a bowl and add hot coffee. Let sit about 1 minute.
- Whisk until chocolate is completely melted. Gradually add oil, stirring until well incorporated. Reserve.
- In a separate bowl, mix flour, baking powder, baking soda, salt, and cocoa. Reserve.
- Using a stand mixer at high speed, beat eggs and sugar in a large bowl until batter is pale and forms ribbons when beaters are lifted.
- Add yogurt and mix at low speed.
- Incorporate chocolate mixture and dry ingredients, alternating.
- Divide batter among three greased cake tins measuring 23 cm (9 in.) diameter x 5 cm (2 in.) high. Bake in oven for about 30 to 35 minutes, or until toothpick inserted in the middle of cakes comes out clean. Let cool slightly. Remove from tins and cool completely on rack.
- Heat sugar and water for 5 to 7 minutes in a small saucepan over high heat, stirring several times, until thick syrup forms.
- Using a stand mixer, beat egg whites in a bowl until soft peaks form.
- While still beating, gradually pour in hot sugar syrup. Continue beating constantly until stiff peaks form.
- Beat in butter cubes one at a time until texture is very smooth.
- Dissolve instant coffee in a minimum of water.
- Gently incorporate coffee and chocolate into buttercream.
- Place chocolate in a large bowl. Reserve.
- Bring cream to a boil in a saucepan. Remove from heat and pour onto chocolate.
- Beat mixture until chocolate has melted completely and glaze is smooth.
- Let cool slightly. The glaze should be somewhat liquid. Add more cream if necessary.
- Place a cake on a serving plate and cover top with buttercream. Place second cake on first and cover top with buttercream.
- Place third cake on top and completely cover cakes with buttercream using a metal icing spatula (run under very hot water, wipe dry and pass over entire cake for a very smooth finish).
- Gradually pour slightly cooled glaze onto top of cake. It should be sufficiently liquid. With the back of a spoon, spread glaze over top and allow to run down cake sides. You may have leftover glaze afterwards.
- Decorate cake with macaroons and serve.
The glaze must be at the right temperature. If necessary, reheat in double boiler so that it is liquid.