French Almond Rum Cake

Preheat the oven to 350 degrees F (175 degrees C). Generously grease an 8-inch round cake pan with butter and line the bottom with parchment; then butter the parchment.

For cake, beat butter, brown sugar, white sugar, salt, and nutmeg together in a large bowl with an electric mixer until light and fluffy, about 3 minutes. Add in almond flour, and beat for 1 minute. Add in eggs 1 at a time, beating well after each addition. After last egg has been incorporated, turn mixer speed to medium-high and beat batter for 3 minutes. 

Add in 1/4 cup rum, lemon zest, vanilla, and almond extract and mix until combined. Reduce mixer speed to low, add in flour and baking powder and mix until just incorporated. Pour batter into prepared pan and smooth into an even layer. 

Bake in the preheated oven until cake is browned and a toothpick inserted into the center comes out clean, 45 to 50 minutes. Cool cake in pan for 10 minutes.

Meanwhile, prepare the syrup. Place water and sugar in a small saucepan over medium-low heat. Cook, stirring occasionally, until sugar is dissolved and mixture is simmering, 2 to 3 minutes. Remove pan from heat and stir in rum. Put pan back over medium-low heat and cook for an additional 2 minutes. Remove pan from heat.

Invert cake onto a wire rack and remove parchment. Leave cake inverted and brush warm syrup over warm cake until all syrup is absorbed. Allow cake to cool completely, about 30 minutes.

For icing, whisk together lemon juice, powdered sugar, pinch of salt, and heavy cream until smooth and combined. If necessary, add extra lemon juice or heavy cream to thin icing to a pourable, but not too thin, consistency.

Place cooled cake onto a serving platter. Pour icing evenly over the cake. Use a spatula or offset knife to smooth over the top if necessary. Sprinkle toasted sliced almonds over icing. Allow icing to set for several minutes before cutting and serving.