In a medium bowl, whisk together flour, baking powder, and salt.
In the bowl of a stand mixer or a large bowl with a hand mixer, cream together butter and sugar until light and fluffy, about 2 minutes.
Mix in egg, grapefruit zest, and grapefruit juice until combined.
Gently blend flour mixture into wet mixture until just combined, taking care not to over-mix.
Place bowl in fridge for about 20 minutes to chill dough.
Pre-heat oven to 375 degrees.
Form balls with 1 Tbsp batter and place on un-greased cookie sheet, about 2 inches apart.
Bake at 375 degrees for about 8-10 minutes, until cookies are lightly golden around the edges. Cool on pan for a few minutes before moving to wire rack to cool completely.
Once cookies are cooled, drizzle Icing over the top and sprinkle crushed peppercorns on top of icing. Let icing cool to harden.