Step 1

Place chocolate bars in freezer until completely frozen, about 10 minute. Remove from freezer, break into rough pieces, and place in food processor with cocoa powder, sugar, cornstarch, and salt. Process until completely powdered, about 1 minute. Transfer to airtight container and store in cool, dark place for up to three months.

Step 2

To make hot chocolate, combine 1 to 2 tablespoons mixture (or more if desired) with 1 cup boiling milk. stir or whisk until combined. To thicken further, return to heat and simmer for 30 seconds until thick and smooth.