Biscoff style (Speculoos) cookies need to be baked and ready before starting with tiramisu cream. Set aside 6-8 serving glasses to serve tiramisu.
In a cold bowl whisk heavy cream to thick and mousse like consistency but still pourable. Absolutely do not whip to a peak! Set aside.
Fill a saucepan with a small amount of water and bring to a boil and then turn to a low simmer. In a bowl whisk together egg yolks and water. Add sugar and whisk well. Place the bowl over the simmering water and whisk constantly until the yolk mixture reaches at least 165°F (74°C). Remove from heat.
Add mascarpone cheese and vanilla extract and whisk smooth.
Add soft whipped heavy cream and gently fold into above using a spatula.
Crush speculoos cookies into bite size pieces and sprinkle a generous layer on bottom of glass. Fill mascarpone cream into the glass nearly halfway.
Sprinkle a second layer of crushed speculoos and cover with remaining mascarpone cream.
Place in refrigerator and allow to firm.
Decorate with additional speculoos and perhaps chocolate decoration and cocoa powder.