Bring all ingredients to room temperature unless otherwise stated.
Line 8" x 5" x 2" cake pan with 2 sheets of plastic forming "t" shape, leaving overhang of 1".
TO MAKE CRUST, place Oreos in plastic bag. Bash into fine crumbs. Add butter. Mix thoroughly. Pour mixture into cake pan. Spread evenly. Press hard so that crumbs are compact. Refrigerate.
132 g Oreos without icing (18 pieces), 40 g unsalted butter
TO MAKE CUTOUTS, cut 8.5 Oreos with 3 cm and 2 cm heart-shaped cutters.
8.5 pieces Oreos without icing
TO MAKE FILLING, soak gelatine in ice water till just soft, 4-5 minutes. Squeeze hard to remove excess water. Place in bowl. Place bowl in freshly boiled water till gelatine is melted, about 5 minutes.
3 pieces gelatine leaves
Add 2-3 tbsp yogurt to melted gelatine. Whisk till even and smooth. Transfer to mixing bowl. Add remaining yogurt. Whisk till even and smooth.
500 g full-fat natural set yogurt
Beat cream cheese till half smooth. Add icing sugar. Beat till just even and smooth. Add about 1/4 of yogurt mixture. Whisk till just smooth. Add remaining yogurt mixture. Whisk till just even. Taste and add more sugar if you like. Scrape down thoroughly and mix through.
250 g full-fat block cream cheese, 120 g icing sugar,
If necessary, chill cream cheese mixture till consistency is like softly whipped cream.
TO ASSEMBLE, break 2.5 Oreos into small pieces. Add scraps from cutouts, or 6.5 broken Oreos.
2.5 pieces Oreos without icing, scraps from cutouts
Pour almost 1/3 of cream cheese mixture into cake pan. Sprinkle with half of cookies. Repeat layering as before. Finish with layer of cream cheese mixture. Bang cake pan against worktop 3-4 times. Cover and refrigerate till filling is set, about 8 hours. Keep chilled till serving time.
TO SERVE, remove cake from pan. Discard plastic lining. Transfer cake to cake board. Decorate with cutouts. Cut with chef's knife, wiping knife clean after each cut.