I have been baking breads and cakes for 20+ years and have relied upon the packages of instant dry yeast. I recently came across a recipe for a Tarte Tropezienne (Daniel Boulud’s Cafe Boulud Cookbook) that calls for 1/2 tsp of fresh yeast. Does anyone know if there can be an equivalent for the instant version? I’m dying to try this.

From the Bread Bible - page 562:

Instant yeast to active dry yeast - use 1.25 times the weight; or, for 1 teaspoon of instant yeast, use about 1 1/4 teaspoons of active dry.

Active dry yeast to instant yeast - use 0.67 time the weight; or, for 1 teaspoon of active dry yeast, use 3/4 teaspoon of instant yeast.

compressed yeast to instant yeast - use 0.32 time the weight; or, for 1 packed tablespoon (21 grams) fresh yeast, use 2 teaspoons instant yeast.