In a saucepan over low heat, melt the chocolate with the condensed milk, stirring frequently.
When the mixture has melted, add the milk, butter, and powdered sugar. Continue stirring until all the ingredients have melted and blended together. Remove from the heat and blend with a mixer with the hazelnut powder to obtain a texture similar to hazelnut paste.
Then return the pan to low heat for about 2 minutes, stirring in the hazelnut paste.
Remove from heat and, for a smooth spread, blend one last time directly in the saucepan.
