- With the rack in the middle position, preheat the oven to 350°F (180°C). Generously butter and flour 12 muffin cups.
- In a small pot over medium-high heat, soften the beets in the butter and lemon juice for 5 minutes. Let cool and refrigerate until room temperature.
- In a bowl, combine the flour, baking powder and salt.
- In another bowl, whisk the eggs with the sugar, lemon zest and vanilla with an electric mixer for 2 minutes. With the electric mixing running at low speed, add the dry ingredients alternating with the beet mixture. Spoon the batter into the prepared muffin cups. Sprinkle with the slivered almonds.
- Bake for 20 to 22 minutes or until a toothpick inserted in the centre of a cupcake comes out clean. Gently remove the cupcakes from the muffin tin without inverting them. Cool completely on a wire rack.
- In a small pot, bring all of the ingredients to a boil while stirring. Simmer for 10 minutes or until the juice becomes slightly syrupy. Strain through a sieve. Compost the beets. Let cool and refrigerate until fully chilled.
- In a bowl, whisk together all of the ingredients with an electric mixer until stiff peaks form.
- Spread a disk of about 3 tbsp (45 ml) of mascarpone cream in the middle of each plate. Place a cupcake in the centre of a disk. Drizzle with beet syrup.