1 Drain sour cherries in a sieve and collect juice. Remove about 225 ml (approximately 3/4 cup) cherry juice. Heat cherry juice in a saucepan and bring to a boil. In a small bowl, stir cornstarch and a little water in a bowl until smooth. Stir cornstarch into cherry juice and cook until thickened slightly. Stir in cherries and add sugar to taste. Remove from heat. For the dough, mix quark, milk, oil, sugar and salt in a bowl and mix with dough hook of mixer for about 2 minutes until smooth. Sift flour and baking powder over quark mixture and mix until smooth. Draw two hippo patterns, one about 1 cm (approximately 1/2 inch) larger. On a floured surface, roll out a little less than half of dough and place on a baking sheet lined with parchment paper. Place small hippo pattern on dough and cut out.
2 In a small bowl, whisk egg yolk and milk, then brush edges of dough with egg. Push almonds into dough as teeth. Evenly spread cherry filling over dough, leaving a margin, about 2 cm (approximately 1 inch). Remove some dough and set aside for for shaping "ear" and "tail." On a floured work surface, roll out remaining dough and cut out large hippo shape. Place second hippo over first hippo, covering cherry filling. Firmly pinch edges of dough together to seal. Use reserved dough to shape "ear" and "tail." Brush back of ear and tail pieces with egg yolk and press into place. Brush dough with remaining egg yolk.
3 Press raisins into dough as "eye" and "toenails." Bake in preheated oven at 200°C (fan: 180°C, gas mark 3-4) (approximately 400°F), 25 minutes. Place hippo cake on a wire rack and let cool completely. Melt dark chocolate and fill a small plastic bag. Cut off one small corner of bag. Pipe chocolate around edges of cake to complete the hippo. Let chocolate dry completely, then serve.