Here are a few Passover substitutions compiled by food writer Eileen Goltz:
1 cup of flour = substitute 5⁄8 cup matzah cake meal or potato starch, or a combination sifted together;
1 tablespoon flour = 1⁄2 Tbsp. potato starch;
1 cup corn starch = 7⁄8 cup potato starch;
1 tsp. cream of tarter = 11⁄2 tsp. lemon juice or 11⁄2 tsps. vinegar;
1 oz. baking chocolate = 3 Tbsps. unsweetened cocoa powder plus 1 Tbsp. oil or melted margarine;
16 oz. semi-sweet chocolate = 6 Tbsps. unsweetened cocoa powder plus 1⁄4 cup oil and 7 Tbsps. granulated sugar;
14 oz. sweet chocolate (German-type) = 3 Tbsps. unsweetened cocoa powder plus 22⁄3 Tbsps. oil and 41⁄2 Tbsps. granulated sugar;
1 cup confectioners’ sugar = 1 cup granulated sugar minus 1 Tbsp. sugar plus 1 Tbsp. potato starch pulsed in a food processor or blender;
1 cup sour milk or buttermilk for dairy baking = 1 Tbsp. lemon juice in a 1 cup measure, then fill to 1 cup with Passover nondairy creamer. Stir and steep 5 minutes.
When baking or cooking, substitute butter with pareve Passover margarine in equal amounts. Use a bit less salt.
1 cup honey = 11⁄4 cups granulated sugar plus 1⁄4 cup water;
1 cup corn syrup = 1 1⁄4 cups granulated sugar plus 1⁄3 cup water, boiled until syrupy;
1 cup vanilla sugar = 1 cup granulated sugar with 1 split vanilla bean left for at least 24 hours in a tightly covered jar;
1 cup marshmallow cream = 8 large marshmallows or 1 cup miniature marshmallows.