Dissolve instant hazelnut coffee in 1/4 cold milk and set it aside.
Dissolve rice flour in remaining cold milk. Add sugar and vanilla. Pour it in a pot over medium heat, stir regularly. Bring to a boil and stir until hazelnut fereni thickens, about 30 minutes. Add dissolved instant hazelnut coffee and stir well, about 5 minutes.
Pour into martini glass, and place them in the refrigerator for at least 4 hours. Garnish with whipped cream before serving.