5. Into your mixer bowl with the egg whites, add the fresh lemon juice or white vinegar, and whisk to stiff peak stage. Ladle about ¼ of the whipped egg whites into the bowl with the chocolate egg yolk mixture. Whisk vigorously to loosen, and so mixture is very well combined. Add the dry ingredients into the bowl and stir well until smooth
7. Pour the cake batter onto the parchment lined baking sheet. Drop gently onto counter to remove large air bubbles. Place into the middle position of your preheated oven. Bake for 20 minutes. Test with toothpick to ensure cake is done. Remove sheet pan from oven and let cake rest in pan for 10 minutes
10. Pour the room temperature Sugar Free Sweetened Condensed Milk into your whipped cream. Whip at medium speed until combined. Do NOT over whip (may get too buttery). Cover the bowl with lid or cling wrap and put in the refrigerator until needed for assembly
11. Make the Chocolate Glaze by adding the following ingredients into a mixing bowl: add the unsalted butter, heavy whipping cream, baking chocolate, coffee powder and sweetener. Place bowl over a small pot of simmering water (bain marie/double boiler). Cook over medium low heat and until the chocolate and the sweetener have melted and the liquid does not feel gritty. Remove the bowl from the pot. Add the mint extract and the Dutch cocoa powder. Stir very well until smooth and no lumps, set aside to cool to room temperature
12. Cut the sheet cake, dividing into 2 equal rectangles. Place the first rectangle onto your serving tray. Scoop all of the soft serve Mint Ice Cream and spread out evenly over the first cake layer. Place the second cake rectangle on top of the ice cream layer. Press on the surface to make sure ice cream comes to the outer edges. Use an offset spatula to scrape away any extra cream mixture.
13. Transfer the room temperature chocolate glaze into a piping bag. Snip a very small hole and pour the chocolate glaze around the inside of the top cake layer to form a frame. Squeeze the remaining glaze onto the top of the cake to completely and evenly cover the surface. Spread out and smooth with an offset spatula. Cut the rectangle into 2 equal halves and place one of the halves on top of the first glazed slab. Adjust to fit the edges as closely as possible. Trim the edges of the cake