For syrup, combine 1/4 cup sugar, water, lemon juice and 1 teaspoon zest in small saucepan. Bring mixture to a simmer, stirring occasionally. Remove from heat once sugar is dissolved and transfer to bowl. Refrigerate until completely cool.
Preheat oven to 350°F. Line muffin pans with baking cups.
For cupcakes, combine flour, baking powder, baking soda, salt and 1 tablespoon + 1 teaspoon dried lavender in large bowl. Stir to combine.
In large bowl, beat butter and sour cream with electric mixer until incorporated. Add 1 1/4 cups sugar, 5 teaspoons lemon zest and vanilla; beat until combined. Add eggs and yolk, one at a time, and beat until well combined. Add flour mixture and beat on medium for 30 seconds. Divide batter evenly into 24 baking cups; filling 3/4 full.
Bake 17-19 minutes or until toothpick inserted comes out clean. Remove to cooling grid and immediately brush tops with lemon syrup. Cool cupcakes in pan 5 minutes. Remove from pan and cool completely on cooling grid. Brush again with syrup when cooled.
For whipped cream, warm cream until steaming in large saucepan; do not boil. Remove from heat and stir in 1 tablespoon dried lavender. Let mixture sit for 10 minutes. Strain out solids and cool completely in refrigerator.
In large bowl, whip cream and confectioners’ sugar until stiff peaks form. Spread or pipe whipped cream on top of cupcakes.