Preheat oven to 300°F (150°C).
In a spice grinder, combine ¼ cup (50 grams) sugar and lavender; process until lavender is finely ground and mixture is combined. Transfer to a small bowl, and add remaining 1¾ cups (350 grams) sugar, stirring until well combined.
In a large bowl, whisk together 1½ cups (300 grams) lavender sugar, oil, eggs, ½ cup (170 grams) honey, lemon zest, and vanilla until well combined.
In a medium bowl, whisk together flour, salt, and baking soda. Gradually add flour mixture to sugar mixture alternately with sour cream, beginning and ending with flour mixture, whisking just until combined after each addition and stopping to scrape sides of bowl.
Spray a 10-cup Bundt pan with baking spray with flour. Pour batter into prepared pan. Tap pan on a kitchen towel-lined counter a few times to release any air bubbles. (Pan will be quite full, but batter will not overflow.)
Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers at least 205°F (96°C), 1 hour and 12 minutes to 1 hour and 20 minutes, rotating pan after 50 minutes of baking and loosely covering with foil to prevent excess browning, if necessary. Let cool in pan for 20 minutes. Using a small offset spatula, gently loosen cake from center and edges of pan. Invert cake onto a wire rack; gently tap wire rack with pan on counter a few times to help loosen cake. Remove pan, and place wire rack on a rimmed baking sheet.
In a small microwave-safe bowl, heat remaining 2 tablespoons (42 grams) honey on high in 10-second intervals, stirring between each, until loose and fluid. Quickly and carefully brush over warm cake. Let cake cool completely.
Cover cooled cake with remaining ½ cup (100 grams) lavender sugar, gently pressing to adhere.