Preheat oven to 350°. Line baking sheets with silicone baking mats or parchment., In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Beat in egg and vanilla. In another bowl, whisk 1-1/4 cups flour, baking powder, baking soda and salt; add to creamed mixture alternately with buttermilk, beating well after each addition. In another bowl, toss blueberries and lemon zest with remaining 1 Tbsp. flour; gently fold into dough., Drop dough by tablespoonfuls 2 in. apart onto prepared baking sheets. Bake until edges just begin to brown, 10-12 minutes. Cool on baking sheets 2 minutes. Remove to wire racks to cool completely., For filling, in a large bowl, beat butter and cream cheese until blended. Beat in honey, lemon zest and vanilla. Gradually beat in confectioners’ sugar until smooth. Spread on bottoms of half the cookies; cover with remaining cookies. Refrigerate in an airtight container.