Make the cookie dough: In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl, cream softened butter and sugar until light and fluffy. Beat in egg and vanilla. Gradually add dry ingredients, mixing until just combined. Add milk if dough is too crumbly.

Chill the dough: Divide dough in half, flatten into discs, wrap in plastic, and refrigerate for at least 1 hour (or up to 2 days).

Roll and cut: Preheat oven to 350°F (175°C). Line baking sheets with parchment paper. Roll dough to ¼‑inch thickness on a lightly floured surface. Cut into cauldron shapes (or circles with added “handles”). Place on prepared sheets.

Bake: Bake for 10–12 minutes, until edges are lightly golden. Cool on sheets for 5 minutes, then transfer to wire racks to cool completely before decorating.

Make black icing: Whisk together powdered sugar, milk/water, corn syrup, and vanilla until smooth. Add black gel food coloring a little at a time until desired depth is reached. Adjust consistency: thicker for outlining, thinner for flooding.

Outline and flood cookies: Use a fine tip to outline cookie edges with black icing. Let set 10 minutes, then flood the outer area (leaving center open for potion) with thinner black icing. Let dry completely (1–2 hours).

Make green frosting: Cream softened butter until fluffy. Gradually add powdered sugar, cream/milk, and vanilla. Beat until smooth. Add green gel food coloring until vibrant.

Add “potion” and bubbles: Pipe or spread green frosting in the center of each cauldron. Melt chocolate chips or candy melts, pipe small dots over green frosting for bubbles, and let set.

Finish and serve: Add edible glitter, sprinkles, or other decorations as desired. Let all decorations set completely before stacking or packaging.