Preheat oven to 350 degrees F. Line eighteen 2-1/2-inch muffin cups with paper bake cups; set aside. Combine flour, baking powder, baking soda, and 1/4 teaspoon salt; set aside.
In large bowl beat butter with electric mixer on medium to high 30 seconds. Add sugars; beat until well combined. Beat in eggs, one at a time, on low until combined. Beat in molasses and vanilla.
Alternately add flour mixture, buttermilk, and cream soda to butter mixture, beating on low speed after each addition until combined. Stir in 1/2 cup of the toffee. Fill cups 3/4 full. Bake about 18 minutes or until tops spring back when lightly touched. Cool in pans on racks 5 minutes. Remove from pans; cool. Frost; top with remaining toffee. Makes 18 cupcakes.
Brown Butter Frosting
For brown butter, in saucepan heat the 1/4 cup butter over medium-low heat until lightly browned, about 8 minutes; cool. In bowl beat the 1/4 cup softened butter with mixer on medium 30 seconds. Add cooled brown butter; beat until combined. Add powdered sugar, vanilla, nutmeg, and salt. Beat in enough buttermilk until frosting reaches a spreading consistency. Use immediately. If frosting begins to set up, stir in a small amount of boiling water. Makes 1-1/4 cups frosting.