How to Make It
In a medium glass bowl, mix ½ cup sugar, champagne vinegar, pinch of kosher salt, lemon zest and lemon juice until combined. Add sliced strawberries and toss to coat. Place in refrigerator for at least one hour.
Crack eggs into a large bowl and scramble with a fork or whisk. Add ¼ cup of the sugar, vanilla, and heavy cream to the eggs in the bowl and mix until combined. Place sliced brioche in the bowl with the egg mixture and allow it to soak for at least 5 minutes.
In a large non-stick pan over low-medium heat, melt the butter. Once it is melted, place the egg-soaked brioche in the pan. Cook for 2 minutes on each side, or until golden brown.
Remove brioche from pan, cut into halves on the diagonal and arrange on a large serving plate. Spoon all the strawberries and the liquid they created over the cooked brioche.
Garnish with a spoonful of mascarpone and powdered sugar. Serve immediately.